You are absolutely correct Les, I think I may have confused these scenes from those I remembered from other more recent WWII movies, there is a film prop supply company in the UK that has all the correct period vehicles that they will rent out to films and they have BMW R71s that they rent out. These days they could supply a bunch of Chang Jiang 750s which are Chinese replicas of Russian replicas of the same bikes.
I have no problem generally with endorsements, but simply plastering a dead celebrity's name on anything that's not nailed to the wall seems overkill and I feel is in danger of diluting the 'brand' and lessening the mystique. I am a fan of Steve Mcqueen's films and the man was clearly a motorcycle enthusiast like us all here, but I wouldn't buy something just because the executors of his estate licenced his image to promote it and in fact I observe that there is often a considerable premium in price to be paid for a Steve Mcqueen model over a standard model from the same company in anything from crash helmets to sweatshirts, to motorcycles.