The pics I posted above are the M1A2 grenade projector as modified for the 601. Originally there were four clips holding a "pineapple" grenade. These were reduced to three to hold a "lemon" grenade which I unfortunately don't have. The tip-off is the full round fin and the empty threaded hole near the clip attachment.
This is an original M1A2 as used in WWII and Korea. Today the Vietnam war is a distant memory even to those who were there, but less than ten years separated the two conflicts and many of these were still on hand in the early 1960s.
Attached File
If you decide to assemble and launch one of these(with an empty grenade of course) you will need to get some grenade launching blanks which are considerably more powerful than regular blanks. I'll dig some out tomorrow and post a pic with the headstamp.
Also, do not launch from the shoulder. Put the butt on the ground.