[rotorwrench]

The change over to rotator valves in 1951 was what made the clearance change as was previously mentioned. If you are running earlier non-rotator valves with an EAB or 8CM cam or what ever stock grind then use the earlier clearance specs. If using the rotator valve, spring, & keeper assemblies with a stock grind cam then use the later 1951 clearances. Aftermarket cams are not included in this recommendation.