Wrencher88 -
I posted a similar question on Stovebolt in 2011 about the valve cover on my '54. "CrankyOldDude" responded with a good answer. Since you are in California, perhaps his answer applies to your truck, too.
"... AC (AC spark plug of General Motors Corporation) California State Approved crankcase ventilation system. California required most 1950 and later cars and trucks to be retrofitted with a PVC system when a used vehicle was sold. The program originally started from January 1, 1964 and ran through January 1, 1966."
Full text of CrankyOldDude's answer My original question and photos- Lonnie
