That is an interesting photo, actually. Taking you chaps as being of standard build and height and also the fact that the gun is on stilts that lift the wheels off the ground by, what, an inch? It is interesting to note how tall the gunshield is. Most models depict the crew huddled, crouched low behind the shield, which I have no objection to at all, it is what we'd all do in a combat situation, but the shield is always represented as only just covering the head of a crouching crewman. I wonder if that is how it would actually be or if said crew would have greater cover, as this photo seems to suggest?
Doesn't help a lot because that photo is also wrongly captioned. The Austrian M40 was a recoilless rifle. I think the detailed comment underneath is correct, it's most likely a modified version of the PaK 40 used post war by the Austrian Heer.