If you can't get the pinion out, what were you going to use in the new housing?
You know how to set backlash and all? I would personally just take it to a differential specialty shop. Thy can probably get the pinion out in no time.
If you want another rear just buy a complete used one from a 99-94 V6 and swap it in. Craigslist, junkyards, check for a LKQ in your area, or car-part.com
1990 GT 5.0 - H/C/I
2003 GT - bolt-ons, 87 octane, 252/298 rw