You speak of blasphemy!!!
Frankenstang pretty much has what you're describing, except it was an '80 Capri done up more like a '90 Saleen (done by her ex). Still has the Capri fenders, but everything else is '90 Mustang with a Saleen wing and front airdam. She's received nothing but headaches from folks on various message boards, and she hates it.
Capris are rare enough as it is, and there is NO aftermarket supplier of Capri-specific parts - NONE! **DO NOT** hack up a Capri or waste its fenders (or other parts) on a dime-a-dozen Mustang!
If I had the money, and if that Capri was closer, I'd be all over that in a heartbeat. That thing has SOOOOOO much potential...