A few notes. All of the spark plugs that pre-date 1947 are what are termed "separable" plugs, i.e., you can actually unscrew them into their component parts. The 1947 spark plug represents a transition to "integral" spark plugs than cannot be unscrewed. These are the types we still use today (so much for technological innovation). At a bare minimum, if you see a plug that does not look like the ones in your buggy, it is probably pre-1947.