will a 2001 explorer diffirential fit an an 2001 Mustang GT

Doesn't the 01 Exploder have a leaf spring rear suspension? If so, the housing isn't going to bolt into a 4-link Mustang chassis...

Get the Exploder diff carrier and some 31-spline axles (e.g. FRPP M-4235-E) and you should be good to go to use your OE housing.