Not a slant. 1947 boat Engine

Be aware that the flywheel end is the automotive "rear" and I'd guess the prop is drivin off the front. Also be aware it could be either standard or reverse rotation.

I'd first try squirting some oil into the plug holes, cranking it, and running a compression check. If it's been sitting, and/ or others have poured ?? amounts of gas and starting fluid into it, the rings may be dry. I would just change the condenser. "because.". If you don't have the right one, just pull the old one, and if the new one does not fit, install it over on the coil, and to ground

Bear in mind that is probably 6V and who knows which ground polarity. If it has a generator, pull the field wire loose at either the VR or gen, or pull the belt, and pull the "batt" wire off at the VR

It will not hurt the starter to run on 12, but I would NOT leave the coil connected for long. You might scare up a 12V coil and or coil + ballast

I'm no expert on old inboards, or flathead Chryslers. "Generic"