need tips on finding a 8.25 posi

Just start spinning tires at the junkyard. No need to pull the cover on all of them (if that is what your asking). If you spin one tire and the other turns the opposite way it is a open diff. If they turn the same way...then you've found a SureGrip

Suregrip = Limited Slip - Mopar
Posi = Limited Slip - GM

Your lookin for a suregrip :D. You can roughly try and wedge something under/stopping one tire and trying to turn it with all your might and just make sure it's not worn out to crap. But tires the same way - Suregrip, opposite - Open. If you watch the driveshaft, count how many times the tire turns per ONE turn of the driveshaft to get a rough idea on the gear ratio. Driveshaft turns once, tires turn 3 1/2...your lookin at about a 3.55.

Hope it helps.
-Mike