91 GMC Crossmember
 

So I put a 454 with a TH350 trans in a 91 GMC. The headers and the crossmember are almost in line with each other and not looking like a 3 inch exhaust will work. I found a universal crossmember from Summit pretty reasonably priced but it says it's a 3 or 6 inch drop or flat. I have no idea how much of a drop if any is needed. Or how wide it needs to be. Any advise would be most greatly appreciated.

Re: 91 GMC Crossmember
 

Been a while but here I go.
If I remember right your current crossmember is flat. You want to think of the drop as a lift. Use that drop to mount the crossmember to the upper part of the frame as apposed to the lower part. This will leave your transmission in its current location while moving the crossmember up for clearance. Other options also available.

Re: 91 GMC Crossmember
 

Is your '91 GMC a R/V series or is it the GMT400 platform?

Re: 91 GMC Crossmember
 

I'm sorry, I should have said it's 1/2 ton 2wd short bed regular cab. Don't know why I forgot that.

Re: 91 GMC Crossmember
 

So the universal trans crossmember you found is wide enough for the GMT400 frame? If so, then that would be the way to go with mounting it up at the top of the frame. You'll just have to measure how much drop you need. I would imagine a 6" drop.

Re: 91 GMC Crossmember
 

Should I measure it from the top of the frame to the top of the factory crossmember to get the drop I need for sure? I'm gonna have to check my measurements again on the inside of the frame. The universal mount is 36 inches wide and now I'm not sure if that's for a S-10 type truck of full size. Is the GMT400 the designation for a full size truck? I've never seen that before.

Re: 91 GMC Crossmember
 

Mike, I really like them GForce crossmembers. Went to their site. 87 is the last year for them. The last pic is more along the lines of what I think I'll end up with though.

Re: 91 GMC Crossmember
 

The GMT400 is the platform designation for the '88-'98 full size trucks. The '87-'91 R/V series is basically the same as the '73-'86 trucks. The '88+ trucks have a much wider frame than the '63-'86 ('91) trucks. I would measure from the mounting surface of your trans mount to the top flange of your frame and see what it comes out to be and go from there.

Re: 91 GMC Crossmember
 

Thanks for the info a Capt. I know I'm making all this harder on my self than I need to. Force of habit I guess. Again, thank you.