Thank you very much, Mike B, for chiming in!
Yeah, there's a boss on the left hand side of the dizzy. It's got a bit of grime on it. But I didn't see anything that resembled a stamp. So didn't look any further.
I should wipe it clean, and look, before writing that possibility off tho.

'56? My '64 number tells me plenty about it; the plant, date, whether the cute assembler was wearing a bra that day, and, ... I also saw quite a bit of references deciphering most of the 70's numbers during my research on this (the crate motor) one.
Anyway. I'm glad to get all the input I can on this thing. It's driving me nuts!
Never had such difficulty getting all the details on an engine before.
Thanks again!
Chris