That's not unusual for the tag to be missing, especially if the radiator was ever removed for recore. It's clipped to the engine side of the passenger side tank, alongside where the trans cooler ports would be if for an automatic.

It's really not all that unusual to find an original radiator in an unmolested car. It's just that quite often they don't function as well as they should due to internal or external corrosion or clogging.