Yeah, I noticed the red screws, too.
What exactly is the origin of the "interchangeable" bus stab? I've heard Westinghouse, I've heard Sylvania. I have a Frank Adam panel from the mid-50s that looks like it would probably accept a BR or a QP. And then of course in some panels, a competing breaker will "fit", but only if you really hammer it... not that it will be Code-compliant if you do.