To figure out if the head gasket is breached is fairly easy. I’m sure You can fabricate one of these:
If need be, insert a pipe between the “plug” and nipple.
Remove plugs, turn engine to ignition on cyl. 1, lock engine, fit “plug”, add air.
Remove oil fill cap, airfilter cover, release any pressure in cooling system, but put cap back on.
If coolant hoses gets hard, headgasket bad.
Noise in the intake or exhaust pipe, bad valves (you can check with a lit cigarette (or, as I prefer, a good cigar) in the exhaust too if in doubt)
Notice airflow out the crank case (removed oil fill cap). Notice to compare with the other cyl.
Rinse and repeat on all cyl.
Easy-peasy.
