Dragonfly carburation II

[Bynorthsea]

After few more session working on the carb I have finally reached the conclusion that it has been 'attacked' sometime in the past and there is nothing more I can do to sort it out. With everything clean, the right jets and set up it still was over rich and unaffected by the air screw. It appeared that the pilot jet was being bypassed, on checking the depth the jet seat the jet was not mating but binding on the thread. Pleased to find a fault a possible solution was to ease the thread and screw the jet further in. This done and after checking I still had fuel to the jet, the bike started but now would only run on full  choke, very disappointing. More checking and scrutiny particularly of the air screw appeared to show the fuel passage in the body Being closed off by the screw as soon as it was screwed in. Conclusion when it was running rich it was being fed through the bypass in the jet block from the unseated jet, seating the jet meant that fuel could not take that route and was now unable to enter because of the peculiar positioning of the air screw. Can't think of anything else I can do other than replace the carb.
So even if I could get hold of a new 375/7 I'm not inclined to afford the £200. So some questions.
1. Has anyone a useable 375/7 for sale?
2. There are more 375 carbs with a 7/8 bore than 375/7s, would stepping up 1/16 make much difference?
Finally and not worrying about the authenticity debate has anyone any experience of fitting a Dellorto, Mikuni, Beijing etc
Thanks in advance for any help