OK, got home and looked again at the 1967 Osborn Body A.M., I actually did seem to read it correctly:
Last page of the manual,in the right column: (best I can make it out)
"8- (C4ZB-65104A76) DECALCOMANIA - DEALER INSTRUCTION, ADHERED
TO THE LICENSE PLATE AREA, SEE VIEW "B" (FOR DUAL EXHAUST
SYSTEMS ONLY )."
Now, other years (or earlier years) might be different instructions and nothing preventing assembly workers continuing old habbits from the earlier years. I'm not saying that other (67) single exhaust cars didn't get them but it looks more like they should NOT have recieved them, even if they did.
Just my opinion and I am no expert, just trying to help out with what I found in research.
I looked up the decal engineering number in GOOGLE and noticed there had been some troubled discussion over at the VMF forum several years ago. It doesn't sound like something everyone agrees on at this time.
http://forums.vintage-mustang.com/vintage-mustang-forum/496980-my-first-mca-type-show-how-refresh-exhaust-manifolds-2.htmlRichard