Mine has the PD emissions sticker. I suspect the PC may be for full size Pontiacs with the 400 4 barrel.
The PR air cleaner is the one for a '68 Firebird 400 4bbl equipped with the code 731 heavy duty air cleaner option and uses an A279C AC air cleaner. There should also be an additional label for the PP standard air cleaner using the AC A212CW for the 400 4bbl. Examining the two elements, the A279C looks like a A212CW with an additional foam wrap around it.
