AFAIK, you can remove the head and cam without breaking the cam chain. The head can be removed, valves removed, inspected, cleaned up and rebuilt with new guide oil seals in a weekend if you have parts and tools lined up.
It is highly likely that at least one valve seat will be pitted from sitting for so long and that would require a trip to an auto engine machine shop.
Worn oil rings don't make much difference to compression but check it anyway and do a dry test and wet test (small amount of oil down the plug hole) and see what the numbers are like. If you can do a leak down test, that would give some indication of where the air is leaking out and that would be very useful info.
If the rings are shot or a bore is rusty or scored, the cylinder has to come out but the motor can stay in the frame. Pistons and rings are available on line but that takes it past a weekend job in all probability.