A boat that size has probably been kept in the water. So, blistering is a question as well as the usual transom/stringer rot. And drivetrain corrosion is a concern--sterndrives don't do well sitting in the water.
Bravo 3s run hot compared to Bravo 1s. Without good drive showers and/or very frequent gear lube changes I'd be wondering how the internals are. Best thing going for those is it might have low hours. Draining the lube, if it is not fresh, might show if there are significant metal shavings or not.
As for those motors, I think the 330/310 difference is just crankshaft vs propshaft measurement of the same beast. I think. Good news is that those don't have a very aggressive cam, so reversion issues are FAR less likely. But compression testing is a good idea for ANY prospective motor purchase.
Best of luck with it. (With that whole 'deposit' thing done, do you still have a chance to adjust price or walk if anything's wrong?)
Mike
"I don't have time to get into it, but he went through a lot." -Pulp Fiction