winterizing procedure would depend on whether it's raw water cooled or fresh water cooled.
If the boat is raw water cooled, what ever you do, winterize with antifreeze so you don't crack the intake manifold. If you just drain the engine, you will need a turkey baster to suck out the water in the intake. There is a large plug at the rear to do it. I have 327Q's and they are fresh water cooled (closed system) but still use antifreeze to winterize. Dave
With my Qs, I removed all plugs (4 on starboard side, 3 on port, plus the one on the circulating pump). Bump the starter a couple of times to make sure all water is out of water pumps. Since the plugs were the brass petcock type, I would leave them out for the winter. If your plugs are the regular pipe plug type going directly into the cast iron threads of the block & manifolds - I would grease the treads & replace (so the threads don't rust) after complete drain. Use a wire coat hanger to unplug any sediment in block and exhaust manifolds. Suck all water out of intake manifold with extraction pump & replace with automotive type antifreeze (doesn't take much).
I put a Tee and valve on the intake hose, put an elbow on exhaust port with a large tub underneath to catch antifreeze. I put a sump pump in the tub and run the hose to the Tee. I plug in the pump, start the engine and can run it as long as I want. I often do this to warm up the engine and change the oil before winterizing. I do the same in the spring to flush out the antifreeze so I don't pollute the water with it. It is also nice to run the boat awhile in the spring to make sure old man winter didn't fuss with things and give the engine a once over while all the engine hatches are up and much more visable. I use automotive antifreeze rather than the RV antifreeze because it has silicone in it to lubricate pump bearings and keep impellers supple. I've only had one raw water pump bearing failure in 37 years and replace impellers every 4-5 years so I believe it works and never have to worry about losing and intake manifold or any other part of the cooling system. Dave