Chris,
here's what I mean in this close up.
at '1' on the rear barrel mount I don't see any circular form in the upper interior corner and the corner seems quite sharp. It also appears to me that there is no quarter circle in the opposite corner of the same piece although slightly more difficilt to make out.
At' '2 on the front mount I do see something akin to a quarter circle.
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What do you think to my suggestion that the rear barrel mount is secured underneath with a single bolt/screw similar to the two on the front and not two flat tabs facing each other as many believe it?