decode this 340

Rocky_JS said
H = 1972
M = Marysville engine plant
340-
3958 = Monday, May 29, 1972
144 = 144th engine built that day, might be missing another number.
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All pretty much spot on except engine plant. M= Mound Road

3975 = 6/15/1972

Seeing it's 8144 it's the 8144th unit that day.