The same PCV valve (GM # 1544935) was used from 1949 through at least 1960 on non Dubl-Duti (non Forward Control, step van) trucks - on all size 6-cylinder engines. If you have an original PCV set-up, it would seem to be a good bet that the 1962 235/261 valve should work OK on the 54 engine.
I have seen only a few GM Chevrolet truck PCV systems up to 1960. I do not recall a connection to a manifold (" . . the whole in the manifold for the PCV valve conversion . . "). There was PCV plumbing connected to the air cleaner, and to the valve cover, and to the road-draft-tube replacement PCV tube.
Your 1961 235 might be a truck engine that was converted to using hydraulic lifters; or, is you engine an automobile engine? Did automobile 235 engines have a PCV option in 1961 (that option is not shown in the 1960 car Shop Manual)?
Do you have a photo that you could post of the PCV parts?
What is the NAPA part number for that PCV valve?
