The term Posi refers to GM Positraction, so technically it was never installed on a a Ford. Gov Lock is also a GM-specific limited slip rear end.
Ford used Traction-Lok for most applications, and for a few cars you could order a Detroit Locker. I've owned cars with Traction Lok, but I don't know how it differs technically from Positraction. I'm sure you can find some articles out there on Traction Lok and then pull the cover and find out if that is what you have.
The Detroit Locker was very uncommon in Fords, and usually only available with 4.30 gear ratio for Mustangs and Torinos.