The tube that passes through the water jacket to oil the rocker arms can develop a leak. Try disconnecting the tube at both ends and putting a little air pressure to it to check for a leak. The upper end of the tube is attached to the oil coupling at the center of the rocker arm shaft. The lower end is attached to the engine block near the exhaust pipe, next to a sheet metal part called the "oil distributor". That device restricts the oil flow to the rocker arms until at least 15 pounds of oil pressure goes to the main and cam bearings. If that tube is clogged, or the oil pressure gets very low, the rockers won't get oiled.

Putting enough air pressure into the radiator to check for head gasket leaks or a cracked head can damage the radiator and/or the heater core. Try bypassing the heater with a loop of hose, and connecting the upper and lower radiator hose nipples on the engine with a pair of flex hoses coupled together. Then plumb an air hose to the engine block coolant drain and put 10-15 pounds of air pressure to the block. If the pressure leaks down, you've got a leaky gasket or a crack somewhere.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
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