In addition to having an expert take a look at this engine, I assume you would
also want a sea trial. The way the engine starts up, or doesn't, and the way
it runs, or doesn't, will tell you most of what you need to know. You could
probably expect some rough starting, followed by either some blue or white
smoke. By time the engine warms up to full operating temperature, the
roughness and smoke should clear up. Find out what the max rpm for the engine
is (ought be in the 3400 to 3600 rpm range) and see if you can pull those rpms.
Listen, and look, hard when you do this.

If it starts and runs smoothly, there is a good chance you will have a boat
with a great engine. If it doesn't, you may want to pass.