Did you verify that the ring and pinion gears have the original matching # gear set etch into both of them? If not do that next scope
If they have them you should be able to get them set up properly up
If not a matching # gear set you are on your own shruggy
Are you using a pinion depth tool or trying to go by the pattern ?

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)