OOORRRRR ...
Now I'm just thinkin outside the box right now so bear with me ...
I focus on getting the dang thing to fit & worry about all yer minutiae stuff later
Just kidding.
I'm kinda leaning towards just drill & tap a hole through the collar (on the under side) for a large set screw. Benefits: hidden (no extra holes), no compromise of strength, gives you your locking option for rattling hitches. Issues: Ya gotta carry an allen wrench with you to remove the hitch.
BTW, Welder Guy has already located the hole for the pin 1/2 inch farther outboard for youse people who really can't stand the idea of me getting any sleep so put on stoopid fiberglass bling stuff that gets in the way of using the hitch for what it's intended for.![]()