Thanks R, I've looked at the picture of the carb flange again and there is the faintest mark after the / which could be a 1 making it /10. I also looked at the various mower and cultivator websites (who knew?) and the Shay range looks very likely, the Shay Rotogardener being a good example of how the worm drive would have powered the cutting head. It also explains the horizontal fitting, the non drive-side crank journal being cottered to fit a pull cord starter. I'm now thinking this is a JAP engine, not an RE product but I'll do some more on that. The beauty of sites like this one is that someone may have an idea of where to look, the internet might make searches easier but as any librarian will tell you, without an index, it's rubbish!
Thanks again,
REgards, Mark