no oil on rocker's drivers side only? 360 magnum

When the engine is cold the bearing clearances are tighter and the oil is thicker. This raises the pressure, you'd think that as the oil gets hotter it gets thinner and would flow better than it would when it's cold through a restricted passage. I think you are losing oil pressure somewhere, it may show good at the back of the motor where the gauge port is but it may not be so good up front due to increased bearing clearances in the cam bearings or main bearings. They could be using up all the pressure and volume before it gets up front.