Just my take but before I put an offer on any of these older boats I’d give the owner some fuel money and get him to take me for a short ride. You want to make sure the engines turn up WOT 2300 rpm with not too much smoke. I don’t care about the BS start up test all these turbo boats will smoke until they get some temp and the crap quality of fuel these days makes it worse. If it won’t turn up you know you have issues that need to be resolved and so does the owner who will be softened up on your offer. We did this when we bought our 50 the engines only turned up 1800 and were blowing smoke. The owner knocked 40k off the price and we never did an engine survey because we factored overhauls in the price reduction. We changed filters threw our gear on the boat and headed to Bimini for the giant tuna run. By the time we got there the smoke cleared up and we were hitting 2300 rpm. Engines just needed to be run. 6000 hours and 20 years later we finally had them overhauled. 71 series Detroits are damn near bulletproof unless you run them out of water or oil. Even hurt they will keep on running.