So your saying that because there isn't a picture of one it never happened?? I've seen several post war photos of them mounted on jeeps, and by post war I mean 1950, but the jeep, mount, and weapon were the exact same configuation as what was used during the war.
You seem real intent on picking this whole thing apart, after I've provided AMPLE information suggesting that the designers of the weapon intended for it to mount on a jeep. Either that, or you just haven't read anything about it.
FACT: The M20 75mm recoilless rifle did see action in WWII. US 6th Marine Div used it on Okinawa for bunker busting.
The M20 was designed from the start to use the M1917A1 machine gun mount as the firing platform.
The M1917A1 mount was designed to be used from a ground tripod, or a vehicle mount.
The M1917A1 mount was used extensivly during the entire war mounted on jeeps
There is photo evidence of the M20 being used on this mount and having been mounted on jeeps.
But if you really need to see one mounted on a jeep in WWII, here you go. 6th US Marine's on Okinawa 1945. That is an M20 75mm recoilless rifle, in a M1917A1 mount on a Jeep. I got this photo from my uncle Allen. He got it from my great uncle Martin's photo album after he passed away, who served with the 6th Marines in WWII. Not sure what the story is behind this picture or how he got it but there it is anyway.
Here is one in Germany a few years after the war.