One of the things you can do is get a moisture meter and use it to check for moisture in the hull. Specifically, you should check the transom, stringers, deck and hull. The first things that rot out on these old boats are the stringers and transom.
As for the engines - run the boat on the water. Check the pressure gauges to make sure they look good. Also watch the temperature gauge - too hot/cold could mean problems. Check the bilge before going out on the water. Make sure it's clean. Then check it when you get back - make sure there is no oil in the bilge. There should also be no water in the bilge. Check the oil dipsticks to make sure the oil looks to be the correct color.
As for the outdrives, make sure there are no cracks or welds. There might be some peeling of the outer skin - I've seen that but have been told that's not really structural. Also, make sure nothing is bent, i.e. the outdrive hit something.
Hope this helps!
