Carburettor Spares

[funf]

Hello,
I hope I can find the answer to a little problem that I have with my Model A. Having trawled the search engine here plus my own observations, I believe that my car is suffering from the stuck float valve syndrome. Now normally I would just order some new parts from one of the vendors here in England; however. It is not a normal Model A carburettor that I recognise hence my problem. I am quite happy with the carburettor, it has an adjustable main jet so that with a colourtune plug and by confirming things by reading the spark plug colour, I can get the mixture spot on. It also has an adjustable idle mixture screw so that setting can also be made spot on. I have had as high as 23mpg on a run at 45 miles per hour so economy appears reasonable. ( note that English gallons are different to US ones - 1 imperial gallon = 1.2 US gallons).
So to my question, can anyone please tell me the model of carburettor in such detail that I can order spares, and also vendors.
Identifying mark is solely on the side adjacent to the engine and says " Zenith made in USA". No other discernible markings. I have some images and an exploded diagram that I found on the internet that seems to match what I have.
Thanks in anticipation,
Stuart

ps for some unfathomable reason It seems I can only upload one image at a time, I hope this one is sufficient, or maybe some person cleverer than I can tell be how to upload multiple images.
Stuart