Latest generation rear bumpers only have 4 holes in common with the older generation trucks. So even though the old brackets mount on the bumper they are in the wrong spot and position the bumper in the wrong place. It's not terrible to make new brackets though.
From 99+ trucks or whatever with the integrated seatbelts are not a direct swap into a single cab. The seat brackets are totally different, and the old brackets do not bolt on the new seats... Just in case you were wondering... But they were totally worth the effort to swap into my 94 single cab. No more stupid broken B pillar belts, no more crappy cloth, and no more crappy light grey.
The 01ish 8 lug aluminum wheels will hit the flange on the rear drums of the 8,800 GVWR 2500 trucks. They are wider, and all the width is on the inside of the wheel. I put the rear axle on stands, put it in first, and took about .125 out of that flange with an abrasive wheel. It was pretty easy, and really didn't take much time.
So far I am 0 for 3 on new stuff being a bolt on :tonka: