i run a 1987 ford mustang in the SCCA and it has the 7.5 rear end with 4:10 gears in it, i was wondering is there a posi unit out there made for this rear end or should i go and get the 8.8 rear end?
Ford made a Trac-Loc for the 7.5 It's found mostly in ARB (Aerostar, Ranger, Bronco)applications. They're scattered across ebay all the time. It's where I got mine. They can also be found in j-yards underneath the aforementioned vehicles. The diff tag will have an "L" separating the numbers in the gear ratio. The rebuild kits are also still available and oddly enough they're more expensive than the 8.8 kits.
Auburn or someone like them makes a really sweet aftermarket piece if budget allows. Check em out.