Need help with ford 8.8 rear

So I got this 8.8 from a member on this forum, and it was already chopped and rewelded for my 66 Dart. The pinion was not removed, but the carrier was when I got it. New bearings and seals have been installed.

The problem I'm having is when I go to put it back together. I got a shim kit that uses a couple of thick shims and several thin ones. No matter what I do with the shims, the same thing happens. When I tighten down the right side carrier cap, the carrier still spins. When I even get the left carrier cap snug, it locks up and the carrier won't turn at all. I'm assuming this is bad.

I have the feeling like the pinion isn't shimmed correctly and the ring gear is being pushed down into the pinion gear too much when I tighten the left side (which is the side with the ring gear on it).

Does that sound right? What else might be going on?