I'll throw my swap into the mix. 03 WRX seats into a 99 2.5RS Coupe. I just did this today.
Remove front seats, remove rear seats.
Install rear seat back. It sits up a little higher than the stock one, I'll have to find a way to cover the foam you see in the rear window.
Now I had to firgure out how to bolt the bottom of the back down. There were little black circles covering a secont set of threadded holes higher up, right where the WRX seats need to be bolted down. SO, they bolted down no problemmo!
The rear seat bottom fit just fine, but going from sedan to coupe they aren't quite wide enough. I'm going to use some grey carpeting and cover the ends.
Fronts are easy. I swapped seat belt parts from my old seats to the WRX seats to make sure I wouldnt have problems
Only issue there, is that the plastic bolt covers on the rear floor dont work with the higher wrx seats, but that's
My drivers side inner was off anyway because of my harness mount.