Hello Sgt.Grit,
In my graduation picture from PI in December 1964 we had stacked rifles. The thing I remember most about them beside being a pain in the ass was getting the strap to stay tight. Also if I remember correctly the strap had to be at a prescribed distance from the rifle and pivot points. This was with an M-14. I am sending the picture. I have looked for information on the three DI's on Together we Served but no luck. All three of them would be in their 70's and the two oldest Sgt. Morgan and Corporal Violette might be pushing 80. After all this was on December,16th. 1964. Corporal French in his 70's at least.
"Semper Fi"
Mike
"Death before Dishonor"