Engine Hour Log
Alternatively What about the owners log if he keeps one. I log each trip and record the days events, weather, sea cond, distance run plus hours.
This also helps when comming round to service items.
IMHO, Any engine with only 80 hours on it should look brand new, but if not backed up by service records or other evidence of maintenance, bills & recipts ect. I would suggest Buyer BEWARE!!