I think you're right. The magazine photo isn't dated, but it's a late '40 edition.
I'm building frame no. WM20.2966, which was a Dutch contract M21. From info gained in previous threads, it appears that this bike was one of the first not to be dispatched, being redirected to the War Dept London. These magazine photos are the best guide I've found to the spec these 'UK' WM21s had, esp foot change gearbox. Allows for some artistic licence at least.
If anyone has info about where any of the 7370 contract 'UK' WM21s ended up, I'd be really interested to know...