A word of warning: if you don't know how old the fuel is then drain it out, flush the tank, and fuel lines. Old fuel
will make all of your intake valve stick (open, close, or part way) and cause bent push rods. Then the valves will have to be hammer out. If the fuel smell odd compared to fresh fuel don't use it.
That 75 is not that bad. I would change the oil and filter and drive it for 1,000 miles, just to give the engine a chance to clean itself out. Then I would suggest you do a cylinder leak down test. This will tell you where you are losing the compression. It won't be a lot of air flowing out (with a warm engine you should see vapor coming out) due to the fact the tester is a low pressure version (automotive). If it is the valves (it would be blowing air out the carburetor or the exhaust pipe). Valve lash could set too tight causing the valve to be cracked open, causing a low reading. If it not the valve lash then all you have to do is to pull the heads. If it the rings (air blowing out the oil filler hole) then the whole engine would need to be pull. But with your numbers I would not change a thing, I would just drive it.
If it not broke don't tear it apart. These engine are design to run several hundred thousand mile between overhaul. Beside parts are hard to find.
This is what I been using for a cylinder leak down tester:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
Chances are your engine is fine the way it is, just drive it.
The only thing I suggest you do is pull the valve covers and remove the rocker arm assemblies. The shafts usually fill up with sludge. Make sure the oiling hole (in the shafts) for the rockers is clocked in the right location when you reassemble them. Valve lash is adjusted with a hot engine. While your at it change the thermostat and anti-freeze (8 gallons) after flushing out the cooling system.