With an old boat and a budget the engine choice is less of a concern than
"Soft decks, leaky Windows, moisture saturated bulkheads or sandwich hulls are far more to deal with than an engine that have readily available parts"
These defects can eat months of work , piles of currency and will be ongoing problems as repair can not fix inherent problems..
IF the engine is common . and parts are available , concentrate on the boat issues, not the engine make , if you wish to get off the dock.
A quick look in the boats engine locker , Diesel rated lube oil or car stuff?
On start up from COLD !!!! how long does the white smoke come out the exhaust?
Underway , what temperature does white smoke go away ?
Displacement speed cruiser engines are seldom worn out , most are killed bu poor or non existing maint.