It was the flex plate - now, how bad is it?

Previous thread: Can anyone help me identify this CATASTROPIC engine noise?

As @DieselPro mentioned quickly after I made the post - it was the flex plate making that awful engine noise.

I started by pulling the torque converter cover, which the flex plate had made a deep groove on the inside of.





After sliding under I immediately saw that at least 4 of the 6 bolts on the flex plate obviously wasn't torqued to spec (66ftlbs), because I could turn them by hand. A couple of them had almost worked their way halfway out already.





So, how did the flex plate bolts undo themselves? I don't know.

A couple of years ago the old starter went bad, so I swapped it out with this ...



... sold by a local importer. They didn't advertise it as original GM, but not as a Chinese knockoff either.

This is what it looks like today, attached to the block (I have never shimmed this starter).





The starter support bracket has always been secured to the block. I suspect that the starter, not being authentic GM or shimmed, worked it's way wrong into the flex plate. The damage visible on the flex plate teeth is only on the side towards the starter gears.

The Recommended Course of Action
The way I see it, I have a few options.

The most expensive one being swapping both the flex plate and the starter.

What would you guys do? Is it possible to just tighten the flex plate bolts back to specs and possibly shim the starter?

I would greatly appreciate your two cents!