Trans identification (year)

[Burt Lake Barn]

I recently acquired a 3 speed toploader transmission. The person selling it told me it was a 1939 Merc transmission. When I went thru it, I found it had a later style synchro set in it (may have been updated along the way). At any rate, I wondered if anyone might be able to peg the year for me. On the trans housing above the inspection plate I found the number 7 H C 6 0 7

The shift top plate cover has a number 81-7222

Any help would be appreciated. Thanks in advance.