I'll add a bit too
@QBhoy s post..
Merc did use the 351, it was the MerCruiser 233 (2bbl) and the MerCruiser 255 (4bbl). MerCruiser stopped using any Ford engine in 1977, so they all came out either as inboards or with a drive, like an MC1 or the TR (or TRS).
My main concern wouldn't be cooling. If you're just going to use the engine itself and put it in front of the existing drive, the water coming up from the pump in the drive would be fine. No, my concern is the power of the engine, it's too much (not for the drive), which leads me to think you'll lack enough power at low engine speed to be effective as a stern drive power plant. Remember that jets don't put much load on an engine until they are really revving. A propeller puts load on right from idle. Not enough power in that low range and the boat's going to be difficult to drive. Just ask
@QBhoy
Chris....