Be aware that most aftermarket or upgraded diffs are at least 31 spline so you'll need new axles too. Stockers are 28 spline. Its good to upgrade anyway so it isn't necessarily a bad thing. You can always just get a rebuilt stock diff too and add extra clutches to it while its out if you want as well.
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 ****.