I bought a replacement door for my '86Z and didn't notice till later that the bracket that the inside arm rest/handle bolts to was missing. I can take it off my old one but it's held on with some odd bolt/nut combo with a completely round smooth nut. What's the best way to get these things out. I would like to reuse them if possible.

 

That is probably a pop rivet. Just take a punch or a screw driver if you don't have one and line that up in the center part. Then whack the punch with a hammer till the center section pops out. After that use a chisel to get the round thing off the door.

 

Or drill out the rivits.