Unknown shipping box from a local auction

[TNBandit]

Purchased several years ago at a small local auction. I actually had no idea what it contained until the auction was over and they game me the keys to the padlocks. Inside were several Vietnam era M16 20rd mags, several GI issue M16 Black slings, a tool roll with punches and assorted firearm related tools and a plastic container that had spare M16 parts in it. My full size Colt SP-1 rifle fits perfectly. On the outside of the box were a US postage sticker and a label that's pretty beat up but references a Marine Corps rifle repair depot. I have shown these pictures to multiple people who all say it's not GI issue because they didn't ship rifles individually but was possibly made for a member of the Marine Corps shooting team or something of that nature. Help !