My dad's best quote.
"Don't buy it unless you can steal it"
Small ball peen hammer to test stringer integrity. Should sounds like you're hitting concrete, not a tissue box.
Compression test on the engine, pull the dipstick, look for moisture and/or rust.
What pump?
Look at the electrical under the dash (shocking how often this gets missed).
Look under the hull at the keel in the bow area (common for beaching damage to occur)
Crawl under it and look into the pump.
Take it for a test drive, even if it costs you a tank of gas and a 12 pack of beer.
Best advice I can give you, look at EVERYTHING. If you really want a Chevy, buy a boat with a Chevy, don't settle because it's cheap.
GT