Wow, I guess I'm the only one with bad luck. Bought a boat that had only been sitting in a garage, don't know how long. Had it surveyed and paid a mechanic to run a compression check, found out later he only checked a couple cylinders. Couple of the bores were so rusted the rings wouldn't seal. turned over and ran ok, just got a lot of blow by through the breathers. Had to bore it out to clean up the cylinders. I recommend doing a compression test at the very least and if you can do a leak down.

I'd throw some fresh impellers in it too. Those could incinerate quickly while you are looking around at other things asked cause a mess....

If you are located in an area that frequently gets below freezing temps I would be skeptical. Before you buy bring a mirror and a flashlight and check around the block for any large cracks. Sitting for that long I would imagine if it was bad you might be able to see it.