Like many others, I wouldn't be afraid of the engines because you don't know how many hours are on them. The best advice from what's already been posted, IMO, is:
- Research the type of engine - some have good reputations, some do not.
- Find a mechanic who knows that type of engine very well (ask some questions of the mechanic, don't just take them at face value), and have them onboard for the survey. Make SURE the engines are stone cold when you arrive for the survey, and have the mechanic watch and hear and smell everthing from start-up to full throttle.
- If you're still OK with things after the survey, get an oil analysis. Yes, they are far more meaningful if you have a history of them, but if there is 30 x the amount of copper in the sample that's supposed to be there, you don't need a history to tell you some bearings are on their way out.
- Can the engines be rebuilt "in frame" (I think that's the term). i.e., w/o being removed from the boat? If so, it'll be MUCH less expensive to rebuild one or both than if they have to be removed.
Our first big boat was a 40 year old Gulfstar with twin Perkins 6-354's with over 6,000 hours on them (if the meters were accurate). it's still going strong 4 years and several hundred hours later.