I stumbled upon this thread when searching for data on a Webra engine I have in my posession. It turned out to be a C/L series 1 Webra 5ccm named BigBen5, produced between 1959 and 1963(series 2). I have no idea when they stopped producing the series 1 in favour of series 2.
It is cross scavenged. The piston slopes up in a straight line from exhaust port to the scavenging ports, where it is cut down again to provide the cross flow baffle.
It seems the engine was plagued by heat problems for RC operation, and production was then discontinued.