"I have 21 years to go before
"I have 21 years to go before the government considers me senior
, but:
1. Remove everything OMC related from the boat including engine, drive, steering, controls and gauges/electrical.
2. Buy a donor boat that is Mercruiser powered.
3. Buy a big sheet of plywood, and close in the hole in the transom, then fiberglass it.
4. Then cut the Mercruiser cutout and transfer all running gear from the donor boat including steering system and electrical. Rebuild and replace worn and soft parts as you go (such as bellows)
If your 74 boat uses a high profile OMC drive, you may also need to modify the stringers of the boat hull to be able to mount the Mercruiser drive low enough in the hull to have the vent plate of the drive low enough in the water.
And on the odd boat, you might find the hull won't accomodate this at all so the first step is to get the dimensional install drawings from the Merc manual and do a lot of careful measuring on the hull."