They don't look like the original drums when I compare them to my Z. My '68 Z/28 (I know you are working on a '67) original brake drums only have these "numbers" on them:
Right rear brake drum: 3841177 W-11X
Left rear brake drum: 3841177 W-1X
Also they have a slot in them for adjusting the brakes. I don't see this slot in your photos, but then your photos don't show 100% of the brake drum. Hope this helps.