I went through the same process. My 1972 Sea Ray Has a Mercruiser 165, the GM250. In the winter 2017-2018 the block cracked. It was a choice, buy a remanufactured block, a remanufactured engine, or find a running 165. Since I was in no hurry, i decided to find a running 165. Whew! I must have looked at a hundred of them. They all had some sort of problem and were really only good for parts, but you may be able to find a good block that way. Finally after 7 or 8 months I found a person who was converting his 1978 boat to outboards and agreed to sell me the engine. The marine repair shop finished installing it on Monday (April 15) I haven't splashed it yet but they say it is in good shape. We'll see.
There is an alternative but it is also problematic. The GM 250 was probably one of the most common GM engines up to the early 80's. They put them in millions of trucks. There are auto recycling yards full of them. But then they have to be marinized which is probably just as expensive as buying a remanufactured one.
Any way if you have any other questions I now have about a 11 year history with this particular engine.
PS, I looked at putting a different engine in, but if you have a pre alpha sterndrive you may have to install a new sterndrive because the bolt patterns won't match up, and if you put in a much higher horsepower engine the old sterndrive can't handle the torque.
so the block is done. im having a hard time finding a replacement engine. what are my options here? what engine would go in easy with little to no modification? any help is appreciated.