from the information I have: December 1967
Guess you meant to write 1966 rather than 1967. Hope this is correct or we will need to alter/rewrite some of this thread
If for pictures and or locations for all of the engine compartment decals/stickers search turned up some of the following which would apply to your car originally as well as many others. Search words were "67 decals"
https://www.concoursmustang.com/forum/index.php?topic=27104.msg166291#msg166291https://www.concoursmustang.com/forum/index.php?topic=27097.msg166278#msg166278Sometimes you can find pictures to answer your questions in the Unrestored Picture Threads listed by production year. You can find them lower down the list on the main page.
As often mentioned in this sort of thread we recommend that you don't buy one of the decal "kits" sold by many vendors just because these are often the lowest quality and they typically include a number of decals that are not original to your or other owners cars.
Assuming that you meant that you have a NJ built 67 Mustang completed in December 1966 here are just four pictures of original service decals and how workers placed them. Appears that there were a number of different ways (orientation) that the worker on each shift choose to apply this specific decals if they even considered it. They might have given it some thought since its rarely applied like the assembly manuals/Ford engineers in the big office, wanted them to apply it.

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ECS is a great source IMO for decals. A number of members have donated or worked with them to get some decals made and available or improved over what other suppliers provide. There are also a few areas where addition research should be done to determine if what they have is correct for your specific car and plant. They are few that I'm aware of but just a not of caution and responsibility on each owner or builder like most details.