It's a piece of nylon strapping. I *know* I have some non-sticky velcro around here somewhere but couldn't find it. Still, basically anything that doesn't stretch is what's needed for this mod. It's just shoring up half the elastic to keep it from stretching, yet still allowing flex.
And I didn't get the TD. None of the vendors I reached out to replied... alas. But I'm happy with my magnet hinged one.
My elastic is indeed doubled over and the center snaps are already front-justified. They could probably be more toward the front, but I've never been unhappy with how my shoulder bells hung. This mod was only about keeping the elastic from peeking out under the shoulder bridge.
And they're comfortable, hold their position, and have performed flawlessly for almost 20 troops now. You built good straps.
Now they're just ever so slightly improved.