I have a 1955 Francis Barnett 'Cruiser' powered by a 1H Villiers - theyre very simple, being an english two-stroke, but theyre not really made for off-road as this one seems to have been used for.
I can't tell you much about the James - at least, nothing that isn't in Roy Bacon's Villiers Singles and Twins - but if you want to know about the engine, just ask.
If you're chasing a gasket set, search 'villers 1h' on ebay - notice it's Villers, not Villiers