Firstly, Stuart correctly identified the Mystery bike of a couple of weeks ago as an Argentinian built Tehuelche. This was a 75cc four stroke single with a gear driven overhead cam built between 1957 and 1964, with 5000 models constucted. It was unique in being the only truly Argentinian motorcycle as other bikes built their were licenced copies of other manufacturers' machines.
In addition to the gear driven cam, the engine was also unusual at the time in being completely built from aluminium. There's a Wikipedia entry, and also a Spanish language website about the marque.
This includes a restoration project, including photos showing the constuction of the engine.
Last week's Mystery bike defeated even Stuart. He was right about the Villiers engine, but the bike was built as far away from Glasgow as you can get - Sydney, Australia.
More information on this website which links to details other Australian built bikes.