If your really interested in what the trans came from, Kevin Marti could provide the full VIN and a Marti Report for some cash. I'd almost bet that it ends up being Fairlane Cobra ( or other non Talladega Fairlane or Torino ) as they probably made at least 18,000 non Talladega cars and only 748 Talladegas......
For years 428 Fairlanes and Torinos were viewed by a lot of people as great parts cars for Mustang restorations so not a lot survived the 1980's and 1990's. Even today, It's pretty tough to restore one of these cars and come close to breaking even financially...
JMHO, John