Well... I bought it. I made sure to get to the boatyard early, spoke to the mechanic there, they know the boat well. Said the crankcase filled up with water and the engine won't crank.
Seller said he had it out on the water maybe 10 times since the freeze plug repair. The last time he was out, he ran it until it stopped and had to get towed in.
Batteries are dead so I hook up my jumper box to check the electrical items and I figured what the hell, I turn the key and it started right up and idled smoothly! No strange noises either and had 15 PSI of pressure. Can't call it oil pressure because it was pumping water at the time. I get the boat home and suck out 9 quarts of straight water through the dipstick tube. The remaining milkshake is too thick to suck out so my plan is to get that stuff out, put some clean oil in it and run it for a minute or two. Not running it on the muffs, I don't care if I burn out the impeller. I want to see if it has normal oil pressure, rev it a bit and listen. I think if it gets this far, there's a good chance the bottom end is ok. I'm going to flush out the oil to get all the contamination out and then take off the intake and the heads, looking for a gasket failure.