Ho Otto,
I wish I had info on that particular model, but I don't. It is one of the more contemporary models, and I'm much more familiar with the older versions.
The Mercruiser motors have a pretty good reputation, I've been aboard a friends boat with the 502 versions and they've run the daylights out of those, with good results.
If your boat is in salt water it must have a heat exchanger system. If it does not, then that means raw salt gets into the block, and that is NOT A GOOD THING. The compression readings when tested are more important to be close to one another in relative proximity, than at a particular reading. That is more to do with the innacuraccy of gauges than any thing else.
When testing, be sure you test with a warm motor and with the throttles wide open (with ignition coil un-hooked so the motors don't start!) Beware of potential shock. If all the cylinders are within 15 pounds of one another, the motor should be able to be tuned and run well.
If I find anything on this particular model I'll post it. In the interim, if you have any photos, please feel free to post them here or send them to me at
chriscraftcommander@hotmail.com
regards, Paul