I just did a frame/tub replacement. I was fortunate in getting a salvage unit that had a tub that wasn't useable but had a ton of good parts. As I got into disassembling mine I found part after part that had to be replaced.
I would have abandoned the project if I had just bought a bare frame. I got the frame mounted brake/gas lines, body mounts, shackles, U-bolts, 2 axles, E-brake parts, plus, plus, plus. All of these had to be replaced on mine.
I still ended up with about $2,200 in parts including the frame and a 2nd tub.
Also, be sure to take pictures. No matter how many you take you will NOT have enough. At least get a picture of EVERY connector, whether connected or not. Also, all ground connections, everything under the dash if you are replacing the tub.
I was fortunate and it started right up after I got done. Didn't have any issues except I knocked the coil wire off putting on a ground.
I even got the transmission skid/mount which was bad on mine. Steering sector had a bad u-joint, power steering hoses/metal was rusted beyond use. Get the idea?