Evaluating engines during a boat purchase

" Hi,
I am looking at a boat

" Hi,
I am looking at a boat with twin 350 Crusaders with unknown hours, 1988 vintage. Other than the sea trial, compression / leakdown test and observing the oil pressure and coolant temperature of each engine, what can I do to determine the condition of these engines? Does anyone in the marine industry do oil analysis on private vessels? Do any of you have direct experience with these engines that you would like to relate?
Thanks for your help! "

" Just a general advice is to

" Just a general advice is to check the engines vacuum levels.This can really be helpful trying to gather up facts regarding the state of tune. Check it out with engine warm ,correct ignition timing and one at the time. The actual reading should be high i.e numerically high and equally important is that it does not move around qiuck or erratictly. I think you can say that 16-19inHg would be considered normal in most cases. This is at normal engine idle speed. What happens higher up is not easy to tell in general terms. If the engines are modified the numbers will usually be different i.e lower.
Peter "

One of the 350ci / 270hp crus

One of the 350ci / 270hp crusaders came up with a dead hole at survey. 100psi while all the rest were 170psi. Surveyor and I are guessing that it is a valve related leak as rings would show uniform wear throughout the engine. Hope we're right! Can any of you tell me what I should estimate for a valve job on one head of this engine?