I have a TT AMAC carb that has the three stud flange fitting, not the usual AMAC clip/stub fitting. John Underhill said that it was the only one he had ever seen, but I believe that Glynn Chambers had another at one time. John said that he thought it was made for the 1926 MGP machines built for Noel Mavrogordato and Paul Stables, and never put into production, so very,very rare. The Mavro machine has fairly recently emerged from long-term hibernation, and is being rebuilt by Ian Bingham. He is coming to see me in September, and I will be interested to hear what carburettor he is planning to use… 😉