Sounds like you are relatively right on in size, budget and and capablilty.
Again, find out how the replacement engine was handled and who did it. Might talk to them and/or who ever regularly works on the boat. Dont expect too much but you might gain some info and its only a phone call.
If they froze the block, any chance hard ballast tanks cracked?
Always do a full lake test! Many problems can hide even sitting on a hose. If it is cold, bundle up and offer to rewinterize. It will pay off as will a $150 payment to a local boat mechanic to meet you and look it over if you dont know boats well.
If you are trailering it any distance, make sure the bearings have been repacked, how old the tires are and the last time the brakes were bled.
A $30 vacuum kit from harbor freight, almost any first timer can self bleed in less than an hour. That can tell you how rusty internal brake parts are and will probably easily pay for itself in negotiated price or knowing what you might be getting into.