OK, I finally see the point of contention here.
Sorry, I just immediately looked up the reference without closely examining Nuno's photo, since the photo was familiar to me. Nuno's photo has been retouched, and in more than one place. At the right front corner, (from the perspective of us, the viewer), I now see the "Wheel" on Nuno's photo. This object is not on my photo. There are two other smaller "wheels" a little farther back on the gun carrage. When you view Nuno's photo blown-up, you can see these are rather poorly drawn, they aren't even in the correct perspective. This was obviously a half-baked attempt by some German PK operative to make this weapon appear as something other than what it actually was, in this case, making it appear as some kind of super self-propelled gun. An interesting comparison of photos. Those crafty Germans, can't trust them as far as you can throw a coastal battery!
As a further note, I shouldn't even be looking at this right now as I am heavily sedated from just having had dental implant surgery for a tooth that I managed to blast out of my head. It's little wonder I can't see the obvious. I know, that excuse only goes so far, what about every other day?