Many years experience winterizing in a salt water region...here's my advice:
1) the reason why you should not use the suck the AF up the drive method, is that the raw water will go right out the exhaust manifolds, till the engine completely warms up. Then when the 'stat opens, the hot water in the engine, will also exit through the stat housing. BUT, the stat is cycling so that its not open all the way, all that long. So there is no garantee that it will stay open long enough for all the raw water to exit the block, and for it to be replaced by AF. So you really don't know what mix of AF you have, unless you take a sample out of the block drains.
2) My way which is also the same as stated in both OMC and Merc factory manuals, is to add AF manually AFTER FULLY draining the engine, manifolds and raw water intake hose. I poke all the drains and point that hose down in the blige, to make sure I got as much water as possible out. Remove the lower end of the big hose that goes from the stat housing to the front circulating pump, that holds a lot of water too.
3) I replace the drain plugs after coating the threads with OMC gasket sealer, this keeps the threads from corroding. My plugs come right out even after the engine has sat with salt water in it all season. Do not leave them out, the threads are raw cast iron and they will rust.
4) adding AF: I reconnect the bottom end of the big hose from the circ pump and disconnect the top end at the 'stat housing. Put a funnel in it and start filling the hose till AF runs out the stat housing neck. Engine is now filled
Do the same with each manifold, till you hear AF run out on the ground (why you must use no tox marine stuff). Fill the raw water intake hose till AF runs out the drive water intakes.
I use -100 because it has much more PG in it and the others, start to get slushy/hard at at 10*(-50) and 0 (-60). Never had a problem and my engine inside does not have a lot of flaking rust. You can just drain, but raw cast iron rusts and then the rust starts to clog the smaller passages between the block and heads. You can tell because then you get chronic overheating even when the rest of the cooling system is fine. GM designed these engines not to be run on raw water but on EG antifreeze with corrosion inhibitors. So do what you want, but this way will lead to the longest engine life. Or else OMC and Merc would not bother to put it in their manuals.