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Old 03-12-2018, 05:59 PM   #1
PGG
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So my all original 72 has a replacement engine block. What to do?

So I bought my 72 K5 Blazer 4x4 as an all original truck other then repaint in its original color before I got it.
Turns out the engine block is a 77-78.

So do I rebuild it with?

A. Build with this 77-78 4 bolt main block since I have it? Its standard bore.
B. Put in a new LT1 replacement and TH700 tranny?
C. Find a 72 4 bolt main casting and keep it as close as I can?
D. Buy a new warranted replacement?
E. Just F it and put a big block in it with 500HP?

I am leaning towards option C but no idea how hard that block would be to find and I feel like there is little upside to doing that value wise as I wont lie if/when I sell it anyway.

Thanks PG

PS, yes I am butt hurt if that matters I thought it was the original engine and there is no real going back.

Last edited by PGG; 03-13-2018 at 03:48 AM.
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Old 03-12-2018, 06:36 PM   #2
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Re: So my all original 72 has a replacement engine block. What to do?

“All original” went out the window with the repaint. Numbers matching can’t be proven and means nothing. Do whatever you want to the truck, GM made lots of them.
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Old 03-12-2018, 06:38 PM   #3
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Re: So my all original 72 has a replacement engine block. What to do?

If you can find period correct ,go for it , If it makes you happy !
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Old 03-12-2018, 06:44 PM   #4
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Re: So my all original 72 has a replacement engine block. What to do?

You need to decide how important this is to you.
As Led said....there is no such as numbers matching in these trucks...just dated coded motors.
If this is important to you....a '72 truck engine isn't all that hard to find if you look around a bit, noting that there 10's or 100's of thousands of these made.

I had a '72 truck once that had a late 70's truck engine in it...that was do for a rebuild. As it turns out there was a guy wrecking a '72 with its original 350 in it.
I bought that for $150 and had it rebuilt and put that in the '72.....close enough.

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Old 03-12-2018, 09:06 PM   #5
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Re: So my all original 72 has a replacement engine block. What to do?

Even though I love my Z28 with the LT1, I wouldn't recommend that engine for you. Yes, it's a nice engine, but sooner or later you're going to deal with the Optispark, and that's an expensive repair. The L31 Vortec would be a much better choice. My LT1 is rated at 275 HP and 325 ft/lbs, and my slighty-built L31 (HT 383 cam, dual exhausts, Quadrajet) puts out 330 HP and almost 400 ft/lbs.
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Old 03-12-2018, 09:40 PM   #6
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Re: So my all original 72 has a replacement engine block. What to do?

There are and there aren't numbers matching with these trucks, just not in the muscle car sense. The suffix code on the truck block Denotes the vehicle it came in, just not the exact vehicle. Every truck came with a specifically numbered block that is correct for it's configuration. Any other code means non-orginal engine.

I'm having a hard time figuring what is important to you. I got the impression you bought the truck because it's all original and are disappointed to find it isn't because of the engine. By that I'd say get it right. Find a motor with the suffix code for your year and configuration. Example: TDL means '72 307 2bbl 135hp auto C10 & C20. Now that engine could also be an '80 350 4bbl 155hp from a van.

Then you are pondering all these other options and that makes me wonder what original matters. Are you at a threshold between keeping/getting back to all original (except repaint in original color) or stepping in a new direction? If so, no one can tell you. It's up to you to do what suits your needs.
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Old 03-12-2018, 09:54 PM   #7
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Re: So my all original 72 has a replacement engine block. What to do?

Rebuild this engine. Deck the block and get a stamp that gets it back to whatever the numbers should be. If there is a "350" cast into the block next to the distributor, grind it with a Dremel and then peen the metal to look like cast iron sand texture there.

I'm just kidding. What do you expect the truck to be worth if you do all that, versus just using the block as-is? You are going to have to convince the potential buyer of the worth. Are you planning on flipping it as "original"? One of my younger sisters bought a '66 Malibu back in the '70s that purportedly had a "4-Bolt Main 350" in it (which isn't even close to original). She drove it for years, and when I pulled it to rebuild it, there it was. Small-journal 327. Don't get wrapped around the axle over originality with a vehicle this old, especially a truck. There isn't a market for numbers matching trucks, like Mustangs and Z-28s. This works to your benefit. You wouldn't believe the prices people pay for NOS or supposedly original parts that look like Frankenstein's monster inside, once somebody goes into it. Distributors and carburetors are especially in this category. There is a pile of carburetors with the number for a '69 302 Z-28. They are everywhere on the internet; many more than Holley ever made. ETA: For that particular application
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Old 03-13-2018, 04:26 AM   #8
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Re: So my all original 72 has a replacement engine block. What to do?

I am leaning towards option C but no idea how hard that block would be to find and I feel like there is little upside to doing that value wise as I wont lie if/when I sell it anyway. I am not planning on selling.

Anyone know where a correct late 71 early 72 block would be?
This is a K5 Blazer if that matters for stampings or any truck would work I am not sure?

Thanks PG
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Old 03-13-2018, 07:40 AM   #9
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Re: So my all original 72 has a replacement engine block. What to do?

Tell us what engine and transmission the SPID lists and we can figure which suffix code you need. To me a truck with the engine it came with is far more desirable than one that had one replaced, when it comes to buying an unmolested truck. It could have been rebuilt a couple times, could be from another vehicle, but having it appear to be the engine it came with still in good running condition suggests the truck lived a better life. The fact that most people say they don't care about such a thing and that it doesn't affect it's value says to me the odds are the engine would be the actual original engine since most people wouldn't bother searching out the correct suffix code.

I had three '72 GM 4wd 3/4t trucks, two with 350 4bbl automatic. The Cheyenne Super was off the road for restoration and the Sierra's engine was sick. I took the engine that was just sitting out of the Chevy and put it in the GMC. The GMC still has the correct engine in it. If someone was totally honest with me and told me the engine has correct code but came out of something else, that would speak volumes to me the overall approach that person took toward what they did on that truck. Little things matter and attention to detail make a difference to me. It would also speak volumes of that seller's honesty to have revealed a thing I would otherwise had no way of knowing. And honesty is most important when I buy. I walk away from liars.
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Old 03-13-2018, 10:32 AM   #10
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Re: So my all original 72 has a replacement engine block. What to do?

Here is my SPID. Thanks guys. PG
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Old 03-13-2018, 11:14 AM   #11
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Re: So my all original 72 has a replacement engine block. What to do?

E. I vote for E.
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Old 03-13-2018, 11:41 AM   #12
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Re: So my all original 72 has a replacement engine block. What to do?

First of all that's a great looking K/5...I remember when you got it....!
As far as "originality".... in my opinion that's kind of like beauty....it's "in the eye of the beholder".....
if the engine has been changed (which a huge amount of them have been) then you have to ask...what else isn't "original" to it that you aren't aware of ?

As of late, the highest value K/5 Blazers that have sold at auction have been resto-mods...mostly LS swapped ones.

Now...the one I have is not, and never will be original, I haven't even bothered to check the block #'s...it doesn't matter that much to me as I will be going to a later model LS1 engine and drivetrain soon....my plan is to have a fun-to-drive, reasonable powered, dependable K/5, that I plan to hand down to my grandson some day...

Again....just my 2
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Old 03-13-2018, 02:38 PM   #13
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Re: So my all original 72 has a replacement engine block. What to do?

Quote:
Originally Posted by A1971Blazer View Post
...my plan is to have a fun-to-drive, reasonable powered, dependable K/5, that I plan to hand down to my grandson some day...
Grandpa, is that you?
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Old 03-13-2018, 02:48 PM   #14
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Re: So my all original 72 has a replacement engine block. What to do?

Quote:
Originally Posted by truckster View Post
Grandpa, is that you?
...you're quick......
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Old 03-13-2018, 02:50 PM   #15
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Re: So my all original 72 has a replacement engine block. What to do?

Wanted to clarify option B.....when you say B. Put in a new LT1 replacement and TH700 tranny?

You mean the new Gen5 6.2L found in the Z06 Corvette and ZL1 Camaro, not the LT1 engine found in the early 1990's Gen 3 Camaro?
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Old 03-13-2018, 05:03 PM   #16
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Re: So my all original 72 has a replacement engine block. What to do?

#1

It will never have it's "born with" engine ever again and truck people don't care.
Unlike cars, there was no VIN derivative stamped into the block. There is no difference in value in the '78 motor and a '72 motor.

"numbers matching" is a game for the Corvette, Z-28, Chevelle SS guys to play.
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