Be careful it's not reverse rotation. So far as I know a huge clue is a great big spacer under the distributor I doubt compression is very high. Marine engines are normally a "high load at medium RPM" IE torque and grunt
Small blocks do not use a spacer under the distributors like the big blocks. I have a 68 Correct Craft with a 318 reverse rotation marine engine. I'd agree to check heads and most marine engines are made to run low octane gas. But the internals are as beefy as was available. Like you said "high load at medium RPM" all day long. I have a 440 marine short block with a forged shot peened crank.
