I guess like you said pulling the heads could reveal something. See what the cylinders are like. Though he'll have to remember that head bolts are torque to yield so he'll have to replace the head bolts and gasket if he does in fact remove them.Anyway its very rare that it is completely blocked after some month. I remember a 1930 Nash convertible I bought of a farmer at his barn. This car was parket in 1950 and never used anymore. It was about 15 miles from my house. So I went there in morning with a compressor, tools,battery and fuel and some hoses to give the car fuel directly from my container. Before starting it up I checked for spark and gave some fuel directly into the carb. Car started right up with lots of smoke out back....but it was alive after 62 years at the same spott. Pumped up the tires and we drove it home...was a funny trip as the radiator was without a lock and halve way it started to spitt out water direct into my face as the convertible top was down and all rotten.
I feel sorry for Gbird67. Lots of more work then he thought now. I wish you luck that you quickly find out whats wrong with your engine. Keep us informed