Starter Problems, Please help

Hey All, I have a 1994 Proline with a 5.7 L Mercruiser Bravo stern drive. The engine blew 2 years ago so I pulled it and had it completely redone. Now, when I install the starter ( 7 starters later) the engine will turn over for a few minutes with now problems then there is a BAD grinding sound. So once it starts doing that I stop trying to start it and I pull the starter again and the starter drive is always broke. When I put the starter on the vice and get the jumper cables and make the starter kick in and run, it runs but when you put a screw driver on the spines to the gear you will see that the drive itself is stripped out. This is the 7th starter I have gone through with the same outcome....any help would be great!!

Shim the starter if it is hanging on the flywheel. Flywheel warped?

How much should it be shimmed? We have shimmed it then left it un shimmed with the same result. The fly wheel is brand new?? any other suggestions?

If the engine doesn't start on the second revolution let go of the key.

2 minutes of constant cranking will kill any starter.

First the ring gear on the flywheel on far enough ? Maybe it's to close to the starter.

Whats compression on that bad boy ?

If you need a few minutes of turning it over you have other problems.