T-nuts, and slightly longer bolts worked.
In addition to the hole for the post, I had to drill holes for the teeth of the T-nut, having learned my lesson when modifying a duty holster a few months back: https://pistol-forum.com/showthread....ot#post1535302
The original bracket allows the pouch to be mounted very low, so putting the t-nut close to the bottom of the link is about 1/2" higher, but I think I can get used to that.
Here's some pics:
Now I need to modify two more links.