Here's a bit of food for thought.............WB30's engines during WW2....probably 1941, when the War Office were considering mixing engines of various makes, primarily the BSA WB30 unit and the Matchless unit into various chassis,.............B30 implants included Matchless, Enfield, Ariel and Norton cycle parts..........other hybrids included the Ariel W/NG fitted with a Matchless engine (the very bike owned by my good mate Mick Holmes) plus other combinations...........part of this exercise was no doubt standardisation....but in reality, this eventually resulted in minor rather than major components between the various British manufacturers........

It's possible the plan might have been to have BSA produce the engines and everyone else the chassis...
That would have freed up BSA production capacity (a major arms manufacturer) from a lot of motorcycle related production...

It is interesting that BSA, themselves a sidecar manufacturer, used Swallow sidecars and chassis during the war...Perhaps that was for the same reason...Ian

email (option): ian@wright52.plus.com