I just completed this exact swap so I have a little more insight on this.
Red_LX asked about the inner bumper...the 86 has turnsignal lights in the bumper and they are actually mounted into the metal bumper not the neoprene nose piece. I enexpectedly found that the bumper mounts from the 86 to the 92 I swapped onto are totally different. The shape of the plates, the bolt spacing and even how far they stick out from the core support. I havn't found a solution yet. I think I may have to cut the brackets off the 86 and weld them onto the 92, unless of course someone has a better suggestion. I tried to ask over at foureyed pride but the mods are some real uptite *******s to be sure and locked the thread.
Headlight wiring is gravy. Same three color coded wires on both cars. I just cut the plugs off the 86 and soldered color to color on the 92 harness. There are 2 ground wires on the 86 setup since there are 2 plugs rather than one but just solder them together. I also converted the sealed beam headlights to housings that take H1 and H4 pop in headlights similar to the later models. I used some of those super white bulbs which are wiched brite. I discovered last night that the stock headlight switch cant handle that, it melted. I will be installing relays this evening.
Moving to the rear....the rear bumper is a pretty direct swap but the earlier bumper has 2 more mounting studs that the 92 for some reason. Options are to either remove the extra studs or drill new holes. The rear side mouldings also are slightly different. The 92 piece had three large studs where as the 86 has 2 plus a small metal stud with this kind of snap bushing thing. You need to drill a small hole for the little stud because it is in a different location than the 3rd large stud on the 92 trim.
Thats about all I can think of at the moment.
