So I broke down and paid the $150 for the barrel spring clamp from BMGParts.com since apparently they are very uncommon and I did not find them anywhere else. That was well over double what I was hoping to spend for one, but at least this one is complete and in excellent shape! The pictures I acquired above took all my internet searching skills. There's surely more pictures out there but I don't know what names or differing NSN or Part Numbers might have been used.
So if you ever come across one, even rusty, know it's worth some cash, but try not to gouge too much, eh?
As can be seen, this one had been parkerized and is a bit different than the shiny one I pictured earlier. It's also one solid piece and feels like cast iron. Probably an older style if I had to guess.
The number in the 4th photo below reads: C-1C6513
Since I had never seen nor fiddled with one in person, it threw me for a bit of a loop, until I realized that the tab between the bottom of the clamps with the big bolt was actually just a cut off flange from the top of the passenger gun ring leg, and thus should be removed.
To protect the barrel of the gun, I found that 1" heat shrink fit tightly, but did fit. A little silicone spray helped coax the heat shrink on.
Then on the passenger front gun ring leg, it was interesting to discover how it fit, and the exact shape of the tabs on the top of the leg would not allow the clamp to sit vertical or flop back towards the gun ring, which is perfect as I could tell it would help align the clamp with the barrel of the gun.
I had two options on how I wanted to mount the clamp. The gun ring could be rotated to the side, and then turn the gun and clamp the barrel pointing forward:
Or leave the gun front and center but rotated and pointing sideways - which was the obvious winner.
I had to remove a stop bolt from the cradle to get the gun to pivot far enough downward, and unfortunately it was rusty and broke so I'll need to drill it out and re-chase the threads. Also less desirable, to allow the clamps room to move enough to get onto the gun barrel, the bottom mounting castle nut is left lose and just pinned in place. This leaves the spring clamp fairly loose so it lays down, which means its metal tabs will rattle and bounce on the gun ring leg, removing the paint. At least I know it'll stay down and clear of my garage door opening. I may see if I can glue a piece of rubber or two in place.
As can be seen in the second to last picture above, the heat shrink actually didn't hold up very well and just from a couple test fits already started to rip/wear through. It's a tight fit on the barrel. Though the heat shrink wasn't very expensive. Maybe I'll try two layers next time, or this clear vinyl hose that I also bought, but I think the hose is a bit too thick.