Did a CB750 ignition bracket ever look like that? I don't think so. My guess is it may be a CB750 style early switch, but it was never on a CB750 but something else. Most likely a CB450 of that limtd era.
If it carries a different part number, the pig tail may be of different length and not proper for a CB750 restore. That's just conjecture something to be checked out, I don't know for sure.