Definitely not the Maxon mount. In the Maxon there was a seat for the operator between the guns, initially one on each side, later two on each side, and the four gun mount the guns were mounted directly over each other and staggered to clear the ammunition cans. The mount was used on halftracks and trailers and by the USN on several Essex class carriers.
While it might be a scrounged P-61 upper turret as some posts suggest, in the P-61 upper turret there was a good bit of machinery for training and elevating the guns as well as the ammunition cans that were below the guns themselves. From the picture that machinery seems to be missing, and the ammunition cans seem to be mounter outboard of the guns which was not the arrangement in the P-61 turret. Also, the outer guns seem to be spaced a bit further out than on the P-61 turret.
So I would say that this is an improvised mount. The barrels are aircraft type barrels, not the Heavy Barrel as used by the Army. The mount might be a modified PT boat twin mount, which used aircraft type barrels, with the two outboard guns added.
Too bad the pictures aren't clearer or giving different views.