The pins are part of, welded to, the batents with small bent loops that the bow extensions go through mounted on the upper armor. I'm searching for some original photos and found some I will post later this week. The loops I mentioned can be purchases from Al Steifel. I don't have any to make measurements but can com up with something for you. If Tim Sutter or Mike France is reading this maybe they can take some photos of Tim's M2 and post them here.
Steve A.