FYI, "Positraction" isn't a generic term, it's the trade name for the limited slip differential made by Eaton and used on a lot of older muscle cars. They still make basically the same thing. I have one in my SC, and it's sweet, much better than the Ford unit.
Usually for on-road you want a limited-slip differential, not a locker. The clutches in a LSD respond to engine torque, and lock to prevent wheel spin. This is what gives you a good launch at the track. A locker locks the wheels if one wheel starts spinning. That's what you need in your Jeep if one wheel is on a rock and the other hanging in the air.
Like Ed said, you need a diff with circlip retaining grooves, not one designed for axle C-clips. You should call the company tech line, don't trust what the salesman says - most of them don't know the difference.
Now, about that Eaton Posi - it doesn't have circlip grooves. The shop assured me it would work anyway, but it didn't. So they had to take the whole thing apart and machine the circlip groove into the side gears. This is several hours of labor and tricky machine work - you don't want to pay for this... luckily they had already offered to fix it for free! (But as they said... "never again!")
Rebuilding a Ford Traction-lok can be done for cheap - IF there is no damage to the unit. Often the clutches wear through the metal end plate, and it breaks apart and runs through the spider gears. If this has happened, it's toast. You should also replace your ring/pinion gear in that case. Actually I'd recommend that either way - those 3.55 gears are probably the best $170 I've ever spent on my car.