Are you sure it's not a #1970831 Alternator pulley?

Yes according to the measurements. I'll ask owner to double check diameter and confirm keyway slot.

Someone please correct me if I am wrong but there have been at least a few 67 cars witnessed with and without the part number stamped and as being originals.

I can tell you that every survivor 67 L78 camaro in the reg. that we have seen always has the stamped pulley from an early 4p L78 survivor to a july survivor. But i would never say they didn't come unstamped. Stamped pulleys are tuff to find. La cars may have had a double alt pulley. I've found 2 100ak in 20 years

Luckily I've sourced a stamped pulley (Top pulley). If I can get the current owner of the engine to measure the pulley and check the keyway I can confirm 100% it is a 3844100 (spoiler alert I won't). Bruce (the original owner) did race the car and its not impossible the alt/pulley were changed. I'll be running my stamped pulley on my car for now. It feels like the more I learn the less I know.