Re: New used boat how can you tell what motor you have?
3970010 can be several small block chevy motors. That casting was used for 350's mostly. 3970010 was also assembled as 2 bolt or 4 bolt main.
If it has ever been rebuilt, it can have just about any large journal crank in it and can be several displacements.
I built a 327 4 bolt main in a 3970010 block, and I have an original L48 350 2 bolt main in my 73 Chevelle that is a 3970010 block.
It doesn't really matter what it is, as all external parts are the same regardless. If it runs well and works well, call it a 350.
I see a few unsafe external bits on there in those pics, like a non-marine fuel filter, automotive HEI ignition system, vented breather with no hose to flame arrester. All that is unsafe in a boat. Kinda looks like someone just grabbed a motor out of a car or truck and dropped it in - aluminum intake and all. I would check that rusty water pump and see if it is marine. Marine will have a bronze impeller inside. Car has tin impeller which would probably be gone by now due to rust. Probably an automotive fuel pump on there too - I don't see the yellow safety hose to the carb. Check the starter motor too - probably also unsafe automotive part. If it is marine it will say SAE J1171 on it.
Check the alternator for spark arrest screens too. That Delco should have this screen cover on the back:
