Instruction Manual No.4 for my 1963 T90 specifies the carburettor as an Amal 376/300. Whilst I have an Amal carb, the body is marked RB 928/8. Presumably this means it is a Mark 1 Concentric 900 series with a 28 mm bore. Does anyone know whether this was a later specification or has it been changed by a previous owner for some reason?