I've found it. Carefully camouflaged to look like a very western European sans permis with a dragster-style flip-front it's the Csaszi from József Császár of Hungary. Did the legislation in Hungary support the same type of unlicensed vehicle - niche market at the time? It looks too well-built to be an entirely speculative venture. This could be the Csaszi-2, the only article I could find is a little imprecise as to which one is which and it unfortunately didn't make it into Pal Negyesi's book.