Chev made a major change in the way the rockers are oiled in 1959. Up to 58 the oil was supplied from the rear cam bearing through a 1/16" restricting fitting, then through a steel tube, then up around the head bolt, then to the oil distirbutor fitting between the two shafts which has the loop up and over like you have been talking about.
Starting in 59 chev changed to a pressure oiling system where oil was supplied from the lifter oil gally straight up a new cast-in rocker supply gally in the center of the block, up to the same head bolt as before where a new larger 11/32" orifice is used, and then to the oil distributor fitting between the rockers. The oil distributor is pinched off with no loop over the top. The rockers were also changed. The oil groove on the inside was moved 1/4" off center so the oil hole in the shaft was not lined up with the groove so as to pressurize the whole system.
Sometimes the early oil distributors were pinched off to help oiling but not from the factory.
