I have worn this belt (with the buckle) through metal detectors in several countries, including the US, and it has never set off an alarm. (I got away with it because it was covered with a vest.)
My concern was with the NOS. It will definitely see the buckle and, I presume, the belt itself. If it does spot the belt, but I have taken the buckle off, am I going to be delayed for the pat down?