Here are a couple pics from McCarthy's book:
I still can't find the bulletin or whatever it was that had the info on how/why these were stamped this way.
Someday, maybe.
Anyway, I think this was kind of a standard practice doing it this way, just not sure when they ended it.
(probably when they quit putting that flat boss on the center exhaust ports?)
Later years like from 73 on they stamped the ID's on the upright boss like the 6X - 4, etc.
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John Wallace - johnta1
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