Hello I have a 1978 300 I-6 in a 2wd f150. The factory emissions label on the valve cover says 300 "C" 1X100 D8TE-9C485 AYB. The parts stores around here and on line only ask if its a "B" or "K" code 300. Anybody have this same problem, or can shed some light on what the "C" stands for? California emissions maybe? Thanks

 

These would have been the emissions calibration codes for the 300 six (4.9L) in 1977 - 1978 ..

 

What exactly is the calibration code used for? Is it for smog tests?