On page 150 of the 67 AIM, DWG PREL 12-20, DATE REL 3-1, UPC 11-13, Sheet B6, it clearly shows a tab on item number 3, which is the center grille and listed as part number 3891693. It is interesting to note that the 67 grille does not show up individually in the early (10/1/66) or later (10/1/67) P&A as being available separately. It was only available as an assembly (upper/center/lower) under part number 3905745 and later superseded (12/68) to 3929281. The 10/1/70 P&A and other GM "books" up to 4/83 show 3891693 as a separate item for sale. It would appear the part you bought is a GM brand reproduction of the original without the tab. To answer your #2....One of the ways we are trying to ID the 68 RS grille in that thread is by the mold cavity (between the circles). It may be possible, after some research, to ID the 67 that way.