If it's a stock truck, he's got a limited slip, not a locker.
In any event, he'll need an open diff carrier to replace the carrier (either limited or locker) he's got. Probably not a bad idea to consider new seals and/or bearings. It'll be a partial gear set up as well.
Edit: Oops... . forgot that he'll probably need a set of side and spider gears as well.