How do you stop your starter from grinding and sticking on your Chevy 305?

Two possibles:

It needs to be shimmed. Chances are if it is a replacement starter it needs to be shimmed. you can buy shims at almost any parts store, they go between the starter and its mounting point on the block. usually one will be sufficient.

also possible you have burrs on the flywheel or starter gear that are hanging it up, should be able to tell that when you pull it to add the shim.

I recently had a starter grinding problem with my boat which has a Chevy 305 engine. You could lose a lot of time trying to find the correct shim thickness, not to mention you have the possibility of breaking a bolt off in the engine. I fixed my problem by having the starter bolts just loose enough to move the starter with my hands while I had someone bump the ignition switch. I had to move the nose of the starter down and it corrected the grinding.