one of the side mirrors on the '86 project car was half broken so i decided to see if i could swap some of the old '83/'84 folding side mirrors on. i found that while the bolt/screw patterns are different between the old folding mirrors and the newer fixed ones, both styles of mirror can be bolted/screwed on. the only issue was that there was quite a gap between the mirror's rubber gasket/housing and the window frame. this would allow a ton of water into the door which would probably cause rust issues down the line. since i had a bunch of the folding mirrors kicking around, i got adventurous with the grinder. i found that by trimming 1/8"-1/4" of the mounting portion of the old mirrors, they can fit perfectly on the '85+ doors. i took some pics.
i trimmed approx 1/8" from the long and short arms and the center circle, and 1/4" from the medium arm.
i then chased the threads for the mounting screws with the appropriate 5Mx0.8 tap and blew them out with compressed air. threw them on and they're a perfect fit now. no gap!
while i was on it, i also tried swapping the fixed style side mirrors on the '84 parts car and they bolt on without any mods. so 83-84 flip flop mirrors require this mod to fit 85-87 tercs, but the 85-87 fixed-style mirrors require no mods to fit on 83-84s.