I just read a lot on the forums before I try anything as I hate to spend stupid money. Oh and I have the knack too...another fucking engineer. Anyhow here are a couple sites I think will help you out a lot as I got a ton of info from them myself:
Mustang Brake Conversion SN95Brakes.com
79-93 5 Lug Ford Fox Body Mustang Conversions
Using the SN95 setup you will have zero center cap problems. Where you run into the center cap problems is the old school Mrk VII rotor swap onto the stock Fox spindle. This will only clear a few rims but the 96 and 97 Cobra wheels will work as this is the route I went the first time...what a waste of money that was.
Darren