Identifing a C4 tranny

I'm trying to identify what year my transmission is.
The vacuum module on my transmission is whets throwing me off.
I know its a C4 because of the bolt pattern of the fluid pan.
Looking in the service manual and talking with the parts guy, the module in
the tranny has two vacuum lines and is held in by a bracket that bolts to
the tranny housing above the transmission fluid pan, and because the tranny
mount is in the way I can't remove the module which (I think) I should be
able to remove and replace without pulling the transmission,
The book for a 72 C4 three speed automatic shows only one vacuum line and
threads in above the pan like a fuel filter, no bracket and the parts guy
got what the book shows.
The book shows where it is and mine is in the same place.
My only guess is when they (somebody in the last 33 yrs.) took out the 302
(after cleaning and scraping found the original engine sticker) and put in a
351C they put in the C4 (which should've been a C6).
I have no codes or other plates to identify it except one number
COAP-70027-A which when goggled brings up nothing.
Every thing else on it seems to match the book, I have several bolt holes
missing brackets and the linkage on the tranny has two arms , mine only
needed one connecting to the control lever to the steering colum and works
fine.
I'm not in the mood or need to change it, but am curious.
Any idea what year it might be

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