[87Skier]

I've never found a good way of determining whether or not a certain rear end has a locker/posi/lsd without looking at it. You can try looking at the spid, or the RPO codes in the glovebox, but it would be silly to buy one without opening it up first. Sometimes you can tell by lifting the rear off the ground, but that usually relies on having the vehicle in park, which you probably won't have in a junkyard.

I will say that you definitely need to measure your axle width. I know that the 1988-1998 trucks had wider axles since they used a different backspacing on the wheels.

You can determine axle ratio a few different ways. You can rotate the wheels once and count the number of revolutions the driveshaft makes, or open it up and count the teeth.