if you want a posi, it is a good choice if you do any driving in snow or mud if you only drive on dry pavemant then it isn't a needed thing but doesn't hurt any either other than the checkbook on the first purchase. As far as finding one look for a bronco, as far as I know all of the early broncos had traklocks in them, and I think that continued on through the 79's, and alot of the early 80s also, and alot of them had 3.50 gears so that would solve both of your needs in one shot