Sounds like you know your basics as far as being able to work on the old beast. I would work my way through the three requirements for an internal combustion engine: compression, ignition, fuel, and start with compression. A regular compression test and if all aren't within 10% follow up with a leak down test. If all is well then the expensive tear down and rebuild is off the table and it's a cheaper but sometimes hard to find solution. Since it does run a vacuum gauge can be a very useful tool as it can monitor functions like valves, timing, and whatever it takes to get the vacuum up to at least 18 inches. If anyone in your area has an old engine analyzer scope then it would be a two minute solution but they are getting rare since new vehicles have on board analysis.
