If you are in the midwest, I have heard that Cory Gehling does these conversions.The following is from Dave Doddek's webpage:
Collectors Choice
Cory Gehling runs a specialty automotive shop out of Madison Wisconsin. He services all makes of special interest autos including some of the rare exotics. His specialty is of course the Pantera. He also makes some custom Viper accessories. Collectors Choice provides heated winter storage for many owners. One unique service that he offers is installing the Mustang 4.6 Cobra Engine in Panteras with anywhere from stock configuration to Blowers or full race trim. Collectors choice also provides factory parts and is an authorized ZF service center.
Contact Collectors choice at:
Collectors Choice
6400 Lodi-Springfield Rd
Dane, WI. 53529
608-849-9878
collectorschoice1@prodigy.net