Re: subframe question
 

I have a 57 gmc but it uses the same rad support as a chevy truck, it's Canadian so maybe thats why? the GMC specific parts are like hen's teeth and the GMC sheet metal assembly stuff doesn't appear in the chevy manual I don't think. sounds like you have experience doing this sorta thing so I'm sure you have a plan and will get'er done. the frame drawings will be nice as they show how much drop the frame has from the cab mounts to the rad support mounts and also the dimension between those-fore to aft. the bumper mount dimension is another one. everything seems to be measured from the cab face as a starting point, which is the firewall. kinda like reading a blueprint, you gotta lot of math to figure out the dimension you need. I'm sure you have thought of this already but a new set of cab and rad support mounts would be good to have installed just so you can get stuff lined up correctly. there is a video on youtube showing how to get things lined up and gapped properly, it uses the drivers side front cab mount as a pivot point and shows how to rotate the cab from there to achieve proper alignment of the hood and fenders. it is "old man fixing stuff", google 55-59 gmc truck panel alignment, it's a few minutes of time that may pay off if you are new to these bodies.

Re: subframe question
 

US models 55 to 57 are different

Re: subframe question
 

the whole front cross member is different. it uses a thin piece of rubber and a u bolt down through it with springs and washers giving it a lot of flex.

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55-56 share fenders, 57 is different around the grille area, GMC also has holes to mount the mustache parts and some dimpled spots in the area around the grill. Just info in case you're looking for parts. 58-59 have longer frames from the spring mounts forward and their rad support brackets are further forward, not sure about the GMC compared to check differences there. Some models were fleet versions that used leftover parts from previous years, like instead of 4 headlights they had 2 and a cheaper version of a grille, bumper etc.
Post up some pics of what you have to work with, you have us interested now.

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Thats on chevy.
55 to 57 gmc uses the 57 chevy fenders.

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Ok, I thought 57 was its own identity

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only the hood and grill

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I wouldn't have thought that a 56 used a core support similar to the 47/55.1 trucks.

That would be an ill driving mess with that axle on backwards.

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axle is not on backwards.
tie rod is flipped from rear to front.

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is that an old impala parked next? I would like one for my next project, wife. not so much, haha

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Why would anyone be fool enough to do that and mess up the steering? That will throw the ackerman way off and cause the tires to not track right on turns unless you modify the steering arms correctly to make it right.

Rat rod stuff maybe but not something that one wants to drive right and go around a corner without dragging a tire.

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bel air 2dr sedan

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That will not mess with Ackerman angle.
If so there sure are alot of 4x4 pickups with solid axle that are screwed.

I'm not going that route anyway. Thats why we're discussing the frame splice.

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the tie rod scenario probably has something to do with the power steering box mounted to the outside of the frame. it likely doesn't turn very sharp to the right before the tire rubs. the plan is to splice in a working independent suspension.
I have seen pics of the GMC style rad support but never seen it in person. it seems similar to the AD trucks but more flexible. would the plan be to keep that set up or have a less flexible set up? since the fenders and hood are bolted to the cab it seems like a lot of ability to move at the front would put strain on the fender mounts and hood latch/bumpers. I know it has lived this long like that but just spit balling since we all strive for smaller gaps and better fitment of the body parts than factory.

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the gmc uses rods from the firewall to rad support to stiffen it.
I would thonk the chevy would be worse gap wise since the rad support is held tight to the frame on both ends making it flex with the frame, where as the gmc is only held in the center allowing the frame to twist under it while keeping it in in line with the cab. My gap change should show at the bumper to grill area when the truck flexes instead of twisting the sheetmetal.

I flipped the complete tire rod assembly for oil pan clearance. I moved the engine forward about 2in and down about 1in so I didnt have to cut into the firewall. cut the drag link part off of the steering assembly so it was no big deal to put it on backwards. That idea is going anyway. Now it will be either a front clip or complete frame from 73 up. either way frame needs cut since the wheelbase is diff between the two.

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the turning radius was the deciding factor. Dont know how much you guys with half tons lose but the newer 16 wheels with the front mount box gives me 2 directions left or straight ahead. and that is with 1 1/2 in wheel space per side.

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Just a little bit of trivia.
5.3 chevy, 4l80e with fixed yoke, 99 semi float 8 lug gm rear and I'm still using the factory 55 drive shaft with the factory 55 yokes, shortend a little on each side of the carrier bearing. original size ujoints and carrier bearing. And the factory 55 spring saddles on the 99 rear original 55 springs. I only needed new center pin bolts to refresh the springs. and new spring perches for the 99 rear.

Gotta love how gm used what worked good and didn't change it.

Re: subframe question
 

Simply because 4x4 trucks with the tie rod in front with FACTORY steering arms have steering arms SPECIFFICALLY designed to take that factor into account. The correct geometry is designed into them. As correct as it can be but we all know and understand that solid axle 4x4 rigs eat front tires up o chew them up too. Even my 92 Ranger with the swing axle thingie is hard on front tires. That truck has lock out hubs and gets driven in two-wheel drive form most of the time.

I've delt with a number of T buckets and hot rods that guys reversed the steering arms to the front like that and the issue is always the same, When they go around a corner one wheel doesn't track right and drags or pushes. it isn't all that noticeable with T buckets with rather skinny front tires except for excess wear for the miles on the tires. it becomes a real issue with rigs with wider tires

If you were trying to do a cross steer with a two-wheel drive C-10/20 box you would have been far better off to build, adapt, or modify a steering arm to attach to the right-side spindle and maybe run off the top bolts. That way you wouldn't actually change the steering geometry.

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probably right about the gmc versus chevy rad support mounts. too late for me now, my rad support is built already with the mounts on each side.
maybe the later chevy steering box works on a lifted 4x4 where the tires would clear, not so great on a more stock height truck. lots of guys have got around that by modifying a box from something else bolted to the side where the original box was, so the output pitman shaft is in the same place.

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Not getting into this argument. A directly attached tie rod from one side to the other will NEVER have the correct angles. Front or rear makes no diff. one gives you to much the other not enough. The more you turn the more out of correct it becomes.

I am not using this setup anyway. so lets drop the discussion.

I am going independent frontend so thats what I'm talking about in this thread.

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Was going to do the cpp kit in stock location but the steering gear is on back order estimated delivery of over 6 months from now. not to mention the $600 price. can get frame clip for less than that.

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the newer style box in the old loaction is very close to a V8 exhaust anyway.
I seen a TF truck on a 88-98 truck frame and it fit pretty well. it was on this site. thats a whole frame swap though so more headaches appear as you continue on. my 57 is sitting on a GMC envoy frame and running gear. way to low for somebody who wants a stock height look. kinda low for me too since I used the floor and firewall from the donor. there are guys who do a more stock height though. lingefelter did a 55 on a trailblazer frame, the Erod, if you google it you can see it.

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I thought about newer but the frames get less straight as you get newer.
Got access to a 90's 3500hd but kinda wide with I beam axle and 19.5 wheels. Also got a 91 3500 but it to has alot of bends in it. To do the splice I need a 64 to 87 with 73 up being the best choice.

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have you seen "project Tow-Rat (Lil'Blue) in the projects secton. he used a 1 ton front end on his. he built his own frame, really nice job, but the idea is there for you to see what he did. he is using ton wheels so there is a spacer on the hub to get the wheel where it needs to be, like a regular 1 ton wold have but possibly not as wide of a spacer? ! ton wheels may clear the steering box better, dunno the track width but the tires fit inside his fenders. I seem to remember one that had the cross member narrowe
d. Can't seem to access the code for that memory though, haha.
SGTUSMC is the guy with the 59 on the 88 frame. his is lowered I think though. it would maybe show the bump in the frame and maybe what he needed to do to get it under there. possibly if you don't want it on the ground the frame bump would be workable?
just ideas for you to look at. sometimes seeing how somebody else did something makes you think of a new way to do something on your project. you can search the site for that members build if you think you wanna see it.

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have you seen the gm upfitters site? they have frame drawings from a lot of years. light duty prior to 2013 is a listing there. maybe find some drawings with the GM specs. try the bodybuilder manual on the site and follow to the area you need to go to.