The setscrew and undrilled lift lever pivot suggests that it is indeed a bombsight; Eric's BOS photos http://www.beautyofspeed.com/gallery/linkert/linkert.htm
show all other bombsights to have their R number cast on the side shown in your photo, leaving this one to be a production carb, I would guess. That would seem to narrow it to M53s? I have a pic of a separated M53, but nowhere to post it. It appears to be the same, although there is a wider gap between "Mod" and "M". I cannot read your numbers below that.
I have only held a few of these in my hands, and cannot cite the differences that make an A1, but most parts can be whittled: The HS needle can be trimmed from a common one, and the nozzle isn't difficult if you have one to copy
All I have on the LS needle is a memory blank.
The venturi is the hard part, even if one comes with it, as they invariably have shrank. They do not appear to be swage-able, easily anyway. (One of our Norwegian forum members had plans to reproduce these, and I requested oversized, or unfinished on the OD, as 1 1/2 models suffer the worst from throttledisc borewear. Alas, my stash of oversize discs are only 9s and 12s. I think the M-53 was a different degree?)
Another hard part might be to find a correct late side bowl, although any should service.