David, I know of no method to determine how severely corrosion has affected the inside of a raw water cooled engine block and cylinder heads. If you and your brother have some magical method, please share.
Yes..... some sarcasm.... but all in fun with you. No offense please!
I just hate to see you toss good money after bad!
Most all of our V-8 Marine gassers began their life as automotive engines.
True..... there may be some castings that offer better material for Marine use.
Perhaps similarly to that of the GM SBC, there may be light castings that DO NOT belong in a Marine application.
You can likely search for this info and find it.
Can't help you much..... I'm more into the SBC.
Std Marine Engine is LH Rotation.... same as Car/Truck engine.
Rev Marine Engine is RH Rotation.... opposite Car/Truck engine.
Piston wrist pin orienation is changed, camshaft phasing rotates opposite, firing order is reversed, etc.
Otherwise, these are nothing more than automotive 318's (minus cam profile, casting core plug material, C/R, etc.)
Either rotation (LH/RH) is viewed as though looking at the flywheel end!