Z'ing my G frame - Q's for the welding guru's

Well, I'm to the point where I gotta get serious on modifing my frame. 85 Cutlass G-body frame. It needs to be stretched and Z'ed. I'm still having trouble finding a guy to cut/weld it that I'm confident will get it straight. I may have to prep it myself and haul it to someone else to lay down the beads. Or if I can get a guy with a portable to my garage....

Anyhow, it's a G-body frame and right now my plan would be to use 2x4 3/16 square tube. Basically replace the rails with 17" extended tube rails 3/4" (front) and 1-7/8" (rear) below the current frame - about a 5-6" drop. About a 80" run of rail.

Is 2x4 good enough for a 80" run? Any suggestions on where to cut the frame or ideas on how to weld in the Z's? Right now I'm thinking of just cutting the rails off the frame and boxing the ends of the cut frame. Then adding my Z and square tube onto the bottom of that. Only thing would be I could only fishplate the outside. Is that good? Ideas?

A few pics:
The first 1-2 are the front section, 3-4 the rear:

80 inches of 2X4 3/16 rail is strong. Fishplating is always a good idea for strength.

This is what mine was a last week. I'll have more pics tomorrow when I paint it.





The existing frame is cut and welded..

I'm just trying to get an idea of what you doing

More pics needed - no problem!

The square tube in the pics is just some left over 2x3 I have to show close to where the rails will need to be. The white chalk lines on the frame are where I would like the frame to be lower so that there will be OK clearance in the cab - not sure that will be possible in the back though. Make any better sense?

Some of the problems I see is because of all the non-flat surfaces.

1-2 front, 3-5 rear

Had an idea about how to deal with the rear part. And another pic. [cl

This one explains it well. Cut off the rear flat, and butt that against a square tube cross bar. Then weld the 2x4 tube to that. More of a normal Z in the front.

Not sure if the rear area looks very solid even with gussets. And should I make the cross bar go all the way across or could I cut it off about 10" in?

That looks good. I'll take pics of mine today and show where my cab is going to be mounted. Are you leaving it the same wheel base or lengthening it? The only problem I see is the cross bar in the rear. It may be in the way of the driveshaft being that low. You can always throw another cross member forward a bit. I'm making removable one for the rear that will also be a driveshaft loop.

Do I even need to have the cross bar or would it be solid enough just long enough for both frame and rail to butt to? Then maybe weld in something more solid where the trans mount goes. I'll to do some more measuring on that.

And yes it will be 17" longer. MY 48 Olds has a 125" wheelbase.

It may be strong enough. The original Gbody frame didn't have anything there. Power from then to now. That's the only reason I'm going to put another crossmember in there. some people say I'm doing mine overkill but if I ever want to throw a BB Chevy in mine I don't want to be worrying about it.

Ok changed it up a bit - cut the center crossbar, add some horizontal gussets, and maybe a crossbar around where the trans will be.

Would I be able to safely use 2x3? That would be great, but I'm concerned about flex. It is still a 3500Lb car.

Oh, and I think I've decided to do this in my garage - just have a guy come over to do the welding. I'll find a big generator to use for power if I have too.

I think that should be just fine.