I would also look to see if on the side of the ring gear has a 3 digit # stamped into it and the same # is found on the pinion. It could be on the head or on the side of the shaft, this is to make sure it's matched set.
Just what I was thinking. I've seen unscrupulous guys mix pinions and crown gears just to sell something. Not saying that's what happened but it's the first thing you should check cause if the ring and pinion isn't a matched set nothing you do will make it right
