I have a Burman BAP g/box on my 1937 Sunbeam. I understand that they were also used by Vincent, Ariel Sq4s and Panther heavyweights. I know the Ariel one had a different casing to cope with the wider engine, but also found out that whilst many internals are interchangeable there are several lengths of mainshaft, presumably to suit the various clutch arrangements.
Fortunately my mainshaft was ok though i replaced many other parts (over 800 quids worth
![Shocked :shock:](./images/smilies/icon_eek.gif)
The Vincent owners Club were having new shafts made but you need to get them to check on measurements. The internals of the BAP box are not case hardened which also makes remanufacture a more reasonable proposition. You may find a skilled engineering company with experience of gear cutting etc that would be prepared to make one. Itll be expensive - they always are - but unless you're very lucky, it might be the only option.
Steve