Ok, I have a 91 4x4 that the back half was way to gone for repair, so cut the back half off at upper gas tank crossmember. I got a 90's 2wd truck for dirt cheap, torched the cab and all that off for the backhalf.
Is everone just spliceing them togeather at the crossmember? I was wanting to come above the cross member to splice but don't seem i'm going to be able to. I run a tap line from the back of the cross member to the weld in the frame and there about 4-6" off.

So my qustion is were is everone spliceing these togeather?

 

it is your Project!!

Just do a normal frame splice Where it works for your truck.

Welded and bolted Fish plates

 

aren't the 4x4 and 2wd frames completely different?

 

yes....

 

No not completely.

84-88 are the same from the back cab mounts back. I dunno about 89-95.

The best place to cut them is just at the back of the cab. There the same from there back on 84-88. Make you you cut them straight and measure them perfectly. Butt them up and weld the top and bottom. After that cut you out some diamond shaped plates. Place those on both inner and outer frame sides. Weld each corner of the diamond. Then weld the sides of the diamond although dont weld it solid. It was be able to flex if not it will break. Here's a pic if you don't understand.

 

I know the front halfs of the frames are not the same, but the backs are fro what i can tell. im going to be getting them side by side and see what i can come up with, ill post what I come up with for outher people to use.

 

You never weld any frame splice vertical .

Although on something as light as these trucks you could no doubt get away with it but life time habits are hard to overcome.

But people need to learn these things.