I have some SAE 4” round red-white bi-LEDs, but my Buckstop has 4” round holes so they were just drop-in for me.
I think retaining the stud-mount will be a problem for using bi-LEDs. The stud-mounts are meant for driving/fog lights. There are some red-white bi-LED driving lights available for overseas markets (not sold here though, because front-facing red lights aren’t legal), but I’m pretty sure they’d be too bright to use a rear marker or even brake light. Maybe as a rear fog light.
The closest thing I could find was a combination 3-rd brake light. They’re 6” wide so they might work?
https://www.novsights.com/products/r...C77Qna2H-Y-aHQ