My last boat which I had for twelve years had an Atomic 4. Most of the bolt-on parts were standard automotive items. Ditto for the starter
. Removed it and carried it into the nearest supermarket-type auto parts store. Matched the bolt pattern with a model they sold, and merely checked the numbers and capacity. Took about six hours and it is still working fine now after seven years. The project would have taken less time except for having to cut a wrench in half in order to reach one pesky mounting bolt.