I'm not great with gas engines, but...
Check/repair/replace everything you'd do on your Jeep, including new belts and new anti-freeze (preventive maintenance).
And then check/replace repair cooling
system stuff. If it's freshwater cooled, for example, you would:
-replace the exhaust
risers and elbows and wing plates (I'm told they only last 5 years or so in salt
-clean your sea strainer (periodic service)
-confirm the water
pump is in good repair
-change the raw water pump
impeller anyway (annual service)
-check the heat exchanger
(and probably have it serviced anyway, even if it appears good)
-check and maybe (preventive maintenance) replace raw water
And while you're at it, deep clean (detail) the engine
room and do some touch-up painting on the engines. This is partly for looks, but especially so it's easy to spot future hose-ups (leaks, etc.) before they turn catastrophic.