Starting in 1958 Chev discontinued the rocker supply tube behind the side cover that sent oil to the rockers from the rear cam bearing and brought the oil straight up the center through a new cast in galley. This new galley gets its oil from the lifter supply galley which ALL 235 and 261s know have even if solid lifters were used. If you do not use lifters that are grooved on the outside on these engines the oil is blocked by the lifters and can not reach the center rocker galley.
