Re: What I have
see attachments for heat exchanger. port side of engine.
as for the anti freeze. i've given up on doing lay up that way. i store dry, w/o water. the way i get it is empty of water is ok. per mercruiser, anti freeze would be better mostly because of the corrosion resistance of the anti freeze. i've been reading these winter lay up questions for years and i'm convinced. air don't freeze. i suppose the corrosion resistance of anti freeze is good. but i can't say that i've ever read or heard of a sweet water boat having the engine rust out from the inside out. i suppose it could happen though. the word is get all the water out of the cooling system. then it don't matter, anti freeze or air. your choice and which ever you feel most comfortable with. either way, ya gotta drain the water from it.
if ya do use anti freeze. pink rv w/corrosion protection is the ticket. good to -50*F. i understand there is blue (?) rv anti freeze good to -100*F too. don't know where your at so don't know how cold ya get. we get down to -25*F or so around here on a bad winter. -100*F anti freeze might be worth while, i don't know.