M try last night seems to gone to the wind. Oh well.
Not sure I can add much.
Uni's were good boats. I'm not sure of the year where the blistering showed up. Earlier models, 70's, were not affected but exactly the year split I cannot say. I've seen both and the earlier, non fire retardent resin boats still look good if care for. The fire retardent resin boats can have blisters all over the boat. Even so, it is mostly cosmetic so you have to decide if that is OK.
I will add that if the vessel in question does not have these blisters now it probably missed that resin.
THe 6-71 are good engines and should have a long life at 300HP IF they have been looked after and PROPPED right and operated sensibly, not on the pins. If not then all bets off although that goes for all engines. They are old but parts are usually still available although through FP for catalogs/parts if not DD themselves.
Federal-Mogul Resource Center - Digital Catalogs
If you are considering I would be looking for a DD mechanic now, for service but also for survey. They are around but not like a bunch of years ago.
Ski in NC who posts here and on Boatdiesel is knowledgeable in DD's. Ronald Sparks on Boatdiesel is also good. Both will be very busy now and both are East coast guys but I'm sure would answer some questions.