So, according to my latest thoughts, the gun which started this topic...
http://forum.axishistory.com/download/f ... ?id=163572
.. most probably is the 2 cm Fla-MG 30, a Rheinmetall gun tested by the Reichswehr in 1931-32. It's seen standing on the ground, with undercarriage removed (although 'fenders' for wheels are still visible in the platform). In other pictures it's more often seen on the wheels.
The gun seems to be more similar to the 2 cm MK ST 52 than 2 cm MG C/30.
Regards
Grzesio