I would imagine that the PCV valve is designed in such a way as to extract as much from the crankcase without creating an overly lean air/fuel mixture. A PCV valve designed from the larger 350 might cause a lean condition and a significant reduction in vacuum wiper performance.
I am not sure what is meant by 'tightess' comparison between early and late model engines. They both are very open between the crankcase and the valve cover via the oil drain back holes in the head/heads.
Carl

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission