Nope, that's backwards- - - -the oil distributor restricts the oil flow to the rocker arms until there's at least 15 PSI in the lower end. That's intended to sacrifice the rocker arm shaft if necessary in order to keep the crankshaft and camshaft lubed. The oil distributor is a 2-section item consisting of an inner piece with a spring-loaded valve and an outer cover that bolts on over it. It's located on the outside of the engine block on the driver's side, near the oil pan rail close to the exhaust pipe, and it has a roughly triangular sheet metal cover. The line that enters the block beside it goes to the pushrod cover on the other side of the engine, passing through the water jacket. That's how the rocker arms get their oil. At idle (or spinning the oil pump with a drill motor) there probably won't be enough pump volume to push the distributor valve open and lube the top end. Fortunately, at cruise speed, the pump will deliver more volume (and pressure, hopefully) and push a little oil to the top end. As the main and cam bearings wear, they have more clearance and require more oil volume, which can seriously reduce the oil flow to the cylinder head.
Another possibility is that the copper line that transits the water jacket diagonally to supply oil from the distributor valve to the pushrod valley can get clogged or broken. I've seen those lines break under the pushrod cover and just dump the oil back into the pan instead of lubing the rockers. Try disconnecting the line at both ends, at the center of the rocker arm shaft and down by the oil distributor, and give the line a good shot of carburetor cleaner and some air pressure. If it's in one piece, that might clean it up. The line can be replaced, but you'll need to drain the cooling system first. Removing the line destroys it, so have a replacement kit on hand before trying to take it out.
Some of the resto-ripoff places have a kit to replace that line and its associated fittings. It's made of 3/16" OD copper tubing and that's a little hard to find, along with the fittings needed to replace it. DON'T use 3/16" steel brake line- - - -it will rust out and let coolant get into the crankcase and oil into the radiator!
Jerry
