Idahoan6-0

I have a '92 K3500 I'm working to part out, and I have someone who wants one of the dually fenders. I got the damaged one they didn't want off, as I wanted to make sure I was removing it properly, and it appears to have some sort of self tapping bolts that goes into the fender (?). How are these supposed to be removed? I'm guessing that self tapping screw/bolt is supposed to stay in the fender, but how would i stop those from turning when the nut has a light coating of rust holding it in place? Any help is appreciated.

Thanks for the info, I am looking to run duals. I'm gonna check the body builder manuals for the frame differences, but from what I've seen they seem pretty close. I'm also running with a 6.0 vortec, so power shouldn't be an issue. I can't imagine that axle not being able to handle that, even with the gearing being so high. After some further research it looks like all the dimensions for the actual mounting are just about the same, except the leaf mounting points are about an inch different per side. Is that tolerable or do I need those mounts moved over (or the leafs spaced out from the frame?)? Also looks like I can relocate the spring perches if everything else works together, and it looks fairly easy just takes a bit of time.

Recently I picked up an older '92 k3500, and did a transmission swap. Sadly the transmission I got had already started going out, and with the old motor it's not worth putting more money into it for me. That being said, I'm thinking of swapping the rear end into my 02 3/4 ton. I've heard the axles are different widths, is this true? If so, could I swap the leafs and all from a long bed dually to a short bed? And one more thing- I'm driving down to California shortly to pick up a camper. Well within my 3/4's rear axle capacity. Could I swap the front wheel spacers on my dually to the current rear axle and stick the duals on? With a 16 hour total drive ahead, I'd much rather have the duals for stability in the back and protection from blowouts. Is this something that'd be safe? I'm running short on time with a sliding fiver hitch still needing to get installed, so swapping leafs and the axle before the trip would take too much time. Thanks for any input