It has a cutout like a Dream carb.

But, at the back there is a powerjet setup like a CB72

The bore is 20mm - smaller than a Dream or CB72

It has a single choke lever - no connection for a second carb..

I was thinking C92 or C95 but the mounting flange is not right.
I cannot find anything similar on the CMS parts diagrams.
It's got a square bowl so that probably means mid-sixties. Other than that I'm a bit stumped....
G