I just bought a 72 Blazer. I eventually want to put a 700R4 in it for economy and the lower 1st gear. It has a TH350 right now behind a fairly stock 350 and 3.73 gears, running 33" tires. I'm planning to build a SB 400 for it eventually, but nothing too wild- aiming for 400 hp and 400 ft-lbs. So what are my options for a 700R4, and what mods will be needed? Is the best option to get a complete trans and transfer case? Thanks for the help.

mods, if you think this would be better in engine/drivetrain, feel free to move it.

I did this swap in my 71 PU almost 10 years ago. It was a fairly easy swap, but some things to remember. If you use the 205 transfer case, the input shaft on the tranny has to be changed. I bought mine from Advance Adapters and had the tranny shop install when they rebuilt. Talk to your rebuilder, but some things I recommend is a Corvette servo, 5 planet planetaries, hardened case, and upgraded clutches, and of course the "K" case. I also had the wiring setup so it goes into lockup automatically once it hits 4th. I just had to run a hot wire to tranny. You'll also have to move all crossmembers back 1 1/2" (I think), which means rear driveshaft gets shortened and front lengthened. Had to cut floor a little for transfer case lever, and modify shifting rods and shaft a little. I like it because I can run 90 MPH with 3.73s and 31x10.50s. One thing I was disappointed with is the MPG...didn't gain one! Don't know why except maybe weight and aero package. Good luck1

Defiantly recommend getting it all beefed up for your motor and moving all crossmembers back around an inch.

I put a 700R4/NP208 transfer case in my 79.. I also used the front drive shaft out of the suburban I got the tranny from.. It was an 88 burb.. I had to find a rear shaft because my truck had a NP203 in it which was full time 4x4. Needless to say my milage almost doubled after I was done.. With the front axle unlocked what would you expect. Next I will be rebuilding the carb and hopfully it will improve more.. I don't drive 90MPH with my 373 gears. The tranny is built with the Comercial clutch pack, wider band, corvette servo, reprogramming valve body kit, and heavy duty lock up converter.. I also put in the bigger reverse valve.. The truck can chirp tires with the 1-2 shift.. I am running 32/11.50 on the truck... I wired up the converter to a toggle switch which I control and can lock it up from 2nd gear up.. It is nice to be able to lock up 3rd when climbing the mountain roads. Not off road mind you... I had to get a bracket from an 86 year model truck/van that still ran a carb with the 700R4 so I could hook up the TV cable properly..
This tranny made my truck much nicer to drive on the freeway.. It improved around town also.. If you can get a front drive shaft from a later model burb it should work just fine.. But you might want to measure first before getting one.. I know they bolt right in to a 77 or a 79 year models. Not sure about the pre 73's though..

Couple more things I did was add the biggest external cooler I could since AZ is a little on the hot side in summer and also an external spin-on filter. Probably overkill, but since I completely re-plumbed the cooler lines, it wasn't a big thing to add in. Also, it's the output shaft, not input, that's different for the 205.

I did this swap in my 72 K5. All I did was move the engine ahead 1-3/4" and the transfer case can remain in the stock location. I used the Advance Adapters output shaft and kept my 205. I'm running 4:11's and 33's and a TBI 350. 2000 RPM at about 65 mph. Mileage improved alot over my worn out carb'd 350/th350 and 3:07's. Highway rpm was about the same with either combo, but the truck has way more bottom end now. If you have any questions, ask away.:) Best mod I've done so far.;)