Montynut google Bultaco Monjuic (or montjuic?),most of those later "bully" race motors were dutch creations,whichever factory paid the race team,thats what they would call them,aermacchi also had a twin w/cooled barrels,aircooled radial finned heads, 2 stroke developed by the villa brothers too,
sorry VMX60,don't do that seat,(ossa engineering in the states?)