[J Knight]

The swap is do-able, a friend and I swapped an 84 body on a 73 frame. Here are a few differences that we found=

frame horn ends but you can trim slightly to fit the 81-87 bumper

you will need to use 73-80 body and radiator support bushings, they are frame specific and not cab/rad sup specific. Don't be suprized if you have to slightly relocate the radiator support brackets on the frame(about 3/4in).

73-83 have a slightly different e-brake set up than 84-87 so you will need to use the complete e-brake cable set up for the 80 or the 87, not a big deal just swap the parts set up you choose over.

The 80 should have a right side fuel tank while the 87 should have a left side fuel tank. You might have to drill a hole or two in the frame to swap the tank mounts over but again, not a big deal. Hope this helps.