Yes, this engine’s gearcase does take conventional lower unit oil, not grease. But, you are right, very cumbersome process with just the one screw. Tip the engine up with the screw facing down, remove it and let it drip for a half hour or so, the oil will eventual dribble out.
The tricky part is refilling, because there is no vent screw, as you pointed out. I would tilt the engine up with the screw removed, then use a little oil squirt/pump can to refill the gear lube. Go very slowly, let it sit when it appears full, the air will escape slowly, then you can add more oil…
Again, squirt the oil in there very slowly with a low volume oil squirt/pump can…..
The water level must be a few inches above the gearcase/exhaust housing joint in order for the water pump to pick up water and work properly…
There are four tiny exhaust/water relief holes about half way up the exhaust leg that will spray a very fine mist of water when you are running the engine. Probably won’t be able to see it, but you will feel it if you hold you hand behind the four relief holes…