My motor is a 1952. It has a hydraulic lifter "clean-out" filter screen provision cast into the cases, which is strange since the oil passages for the hydraulic lifters have never been drilled (under the tappet blocks). Panhead hydraulic lifters were moved from the pushrods to the tappet blocks in 1953. This clean-out screen was to filter debris from the lifters. The factory apparently started casting the clean-out into the cases in 1952? I have a clean-out that really doesn't function in the manner it was designed to . . . and since I run solid lifters, it doesn't really matter. Huh. Why do I dwell on such subjects????