Re: anyone know much about the larson 29 cabrio or a good boat review site
Don't assume
Some engines are fresh water cooled, meaning they have a heat exchanger (like a radiator, sorta) filled with anti-freeze and fresh water. MOST engines are raw water cooled, meaning that they're cooled by pumping whatever water the boat's sitting in, through the motor. Larson is no exception to the 'most engines' rule, so most will be raw water cooled.
A pair of Volvo 4.3's (those are v-6's) will be 'adequate' if you don't carry large loads of passengers. The Larson 290 Cabrio (it was formerly the 280 Cabrio- same boat) is roughly the size and weight of mine. With a half dozen passengers aboard I usually wish I had v-8's and (as a result) bigger props.
I don't know where you live, but $31K is a LOT of money for a '97 in 'decent' condition. I would expect it to be absolutely pristine, with a like-new trailer for that price.
My .02