You can get ANYTHING for a 8.8 rearend, going to a 7.5 is like going from a V8 to a V6... Honestly a stock replacement rearend with the clutch upgrade (google it) will hold up very well to as much power as the block can handle. Unless you are going to be doing a bunch of hard launching on slicks I'd just go that route.
2000 Mustang GT Steeda build #48. Bolt ons, suspension, Novi 2000.
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.