Ok, the Norton Big 4 had the standardised elbow connector, and was used on most British bikes, except Matchless, where there just wasn't any room for this type, I have most of the parts and drawings for this type, email me. here a picture of the standard elbow fitting, still available repro from me, but with the newest huge influx of the filters, not too many left!
Lex the elbow I'm using is the original steel one that came with it, as seen on the Indian M20. The problem is that there is a short tube from the carb to the elbow and the thread on the screw on adapter is too big to go directly on the carb, so I've bought one of these ally adapters which has had to have a few thou turned off it. Ron
A trial fit and the petrol cap works ok in this position. Next faze is to respray the tank and finally paint on it's correct census number after 32 years. Ron