I have a pair of mercruiser 1986 300 tempest v-8s. The engine's originally had trs drives, but were converted to alpha setups. My question is one of them needs a starter. Do I need the starter for the trs or aplha engine? Does the starter depend on the bell housing?

TRS setups typically used a top mount starter that was mounted on top rear of the bellhousing. You can't use that type of starter with the alpha. You will just need a typical Chevrolet starter to work with the alpha. Should be 168 tooth flywheel.
Eddie

I noticed there are two different flywheel sizes the engine came with a 12 3/4 and a 14 in flywheel. What's the best wat to tell which one I have? They are 2 different starter part numbers for the two diffrent sizes.

Ok figured out why I needed a start! The body of the starter was +12v when I turned the key! Anyone ever see this happen?? Could this cause any other damage?

Ok figured out why I needed a start! The body of the starter was +12v when I turned the key! Anyone ever see this happen?? Could this cause any other damage?

Ground wire to that engine broken maybe?

Ground was good. I pulled starter off and jumped a wire from starter housing to block and it sparked liked crazy

Any alternator and starter shop should be able to repair it for you