Nice hunting once again Unkie, I can confirm that the "U" in the engine # of my last pickup as being not so much a misprint but just poorly executed, I would say the right hand side of the U is just an imprint from the side of the stamp head as you can see in the pic the left hand side is definatly a 1, so engine #161,127, you can see the 6 has the same thing but just not as pronounce.

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If you dont make a mess you aint making anything.