I decided to clean up the subframe and differential from the red car a little. Just to get some of the dirt off.
Compare that to the subframe and rear differential out of the silver car:
I did note a few differences between the '86 and '89 assemblies. The biggest is the rear swaybar, its endlinks, and the its mounting brackets (I didn't know about the last one). I also didn't know the "covers" for the main subframe nuts were different. It looks like the mounting studs for the covers are further forward on the '86 making the covers "longer" than those on the '89 and thus no swap-able. Hopefully everything else will bolt up just fine.
I also got all the fuel lines out of the silver car. I did find a few other issues I need to address before the swap can be completed. The vapor line from the fuel tank to the charcoal cannister was rotted through in a few places so I'll swap that over as well. That explains the gas smell. The parking brake is also in pretty bad shape so I may swap that too if I can figure out how to remove/install it.