I drew it in AutoCAD but I hadn't planned on cutting off anymore than was necessary, probably off the top and bottom but leaving as much of the vertical portion to overlap as a fishplate further down the frame. The top is the shortbed frame with bedbolt locations, the bottom is the longbed. The biggest issue is the cut needs to happen in the drop down in the frame, which I think sorta helps with the returns on the frame channel as the rear can sit on top of the front top and bottom.

The seemingly misplaced line on the top rail of the middle drawing is the longbed frame angle, showing how much it would have to be spread. This was the reason I was thinking pie cuts.

I don't know if it'll happen, I've got to many other projects, but I know of a under 100k baby blue LWB minus engine and tranny that the body is supposed to be super straight. The 302 & C4 were pulled for another project, I'd like to CV and Mustang IRS it with a Coyote and a TR-3160.