FWIW, I sent the photos of Gene's spur to noted spur expert and author Kurt House, to whom I had previously reached out to request assistance identifying a pair of spurs I had acquired at an auction earlier this year. He has authored and published several books on spurs and has forgotten more about spurs than most of us will ever know...

Once again, he was kind enough to reply:
"Chris: Rarely can I state anything with 100% confidence, but this Chilean spur is an exception. No doubt about it, I can prove it, which is rare.
Kurt House"
Seems pretty definitive to me.