I've been talking to Fullhoza privately and do have some more pictures. Engine is not a really early one, and I suspect a 1926 example although the engine number I have is not a complete one.
Yes, the engine as fitted is for a two speeder with the crank handle turning the cross shaft. As for speed of swapping engines, the hard bit is the exhaust if you are swapping engines of different types. Another engine of the same type though is easy with an assistant, 30 mins might do it, but probably won't as the chances of having to re-make the propshaft length are too great.
The late fifties and early sixties are the danger years for originalty. There were a lot of cheap second hand spares, and owners either weren't too particular, or had some very strange ideas about improvements! The correct stuff was available too.
