A question RE: an odd looking German AA Gun...

[NickM]

So...Another Automatic AA weapon question: Tony Williams where are you?

Anyhow, here goes: I remember watching an old History Show ('Air Power' or 'Victory at Sea', I can't recall which) & I saw a bit about the FIRST Ploesti raid...in addition to some great gun cam film of low flying B24s under fire by fighters (first time I've ever seen German cannon fire striking the ground under an enemy aircraft-remenisent of RAF/USAAF gun cam films from later in the war) I remember seeming some sort of 'Jury Rigged' AA gun on the back of of a truck; it looked like a VERY oversided 20 mm Orlikon:It had a pintle mount; it even had those shoulder braces (I don't really know what those shoulder thingies are called)that you strapped yourself into when you used the 20 mm...the difference was there was no 'snail drum' magazine in sight and the barrel was MUCH longer; any idea what this beast was? Maybe A 30 mm MK103 'converted' to AA usage?
And what are those shoulder thingies called?

thanks, ahead of time

NickM