I just referenced the 48-51 Chevrolet Truck Shop Manual and it indicates that all 235 engines made after '49 no longer had the oil line going from the oil distributor through the water jacket, going directly to the rocker shaft connector.
Instead, oil to the rocker arms was provided from the rear camshaft bearing.
The purpose of the oil distributor has always been for providing more oil pressure to the spray nozzles aimed at the connecting rod dippers as oil pressure rose from higher RPM.
