12B is the earliest X coded Tag found and then not all 12B tags have them either. Heres a CRG link that better explains the X codes. Have to remember the X codes only pertain to NOR tags.
Have the VIN that goes with it? That will tell you if it was a 6 cylinder or V8
<font color="blue"> Decode for body number: 194464
12A = Built the First week of December.
69-12437 = Coupe.
NOR = Built in Norwood Ohio.
711 = Standard Black Bucket Seats.
76-76 = Car Color is Daytona Yellow </font>
http://www.camaros.org/numbers.shtml#XnnCodes