The locking gas cap is not shown in the 1953 Truck Data Book but it is listed in the 1953 Chevrolet Accessories price list.
Nonetheless, it works on all A-D years and models of trucks; and, it is a lot nicer than the commonly available locking gas caps (that have no cover over the key hole).
There is a NOS one on eBay now with a Buy It Now price of $150 (still too dear for me). Is there a reproduction cap like this available?