I wouldn't call an Advantage a "great boat" personally. A good boat yeah. Being as the interior has been done, a lot if sins can be hidden.
These hulls were prone to wood rot because they never used a lot of fiberglass in the interior, this was done to keep them lighter for performance but it does not make a super durable hull.
Grab a small ball peen hammer and tap around on the boat interior where you no there is wood. Obviously not where it will damage anything, it should sound like your whacking concrete, if it sounds like hard cardboard, put your tools back in the box and walk away calmly....

I agree with the $8-9K, but that would be at the high end of the spectrum. I would offer $5k and see what happens.
It all depends on what you want. The open bow conversion does make me squirm too much, you can push/pull and check the stiffness of the bow area, I have seen dozens of these done and done right.
I doubt there is anything really special about the engine, run of the mill stock Indmar. A compression check never hurt anyone...
Don't buy a damn thing without driving it first. Guaranteeing the guy buying the jeep will drive it first.

Good looking boat...
By the way, not hammering Advantage, I knew Harry Christensen personally (RIP buddy) and worked closely with John Sepulvida of Advantage in the mid 90's.
GT