I certainly wouldn't assume a 40 year old marine block isn't thin.
Sonic test the cylinders!

I've never heard of a "marine" block. Maybe that's a Chrysler thing as both the ford and gm "marine" engines are no different than the automobile blocks. Just machined for the marine environment.

Do you have some data to back up the high Nickel "marine" specific casting you're talking about?

unions....the folks who brought you the weekend!