Pics look promising, especially if you can deal with the woodwork (teak) stuff.
I think GBs of those years were maybe fiberglass hull with wood deckhouse? Anyway...
It's customary to have a "marine" survey... which may or may not be sufficient for engine info... and its also customary to have a "mechanical" survey for engines and ideally genset too. Both accompanied by an actual sea trial. Latter with oil samples.
Some money invested there will do three things: help you with the stay or run decision, point you toward what needs fixing first (second, third, etc.), and get insurance and maybe financing if necessary.
Learning basic diesel stuff can be relatively easy, especially since I'd guess those engines are naturally aspirated (no after/inter-coolers, no turbo, etc.). Take a course, read a book (Nigel Calder), etc.
Chesapeake Bay, USA