1967-1970 Shelby Mustang Cobra Single 4 Barrell Original Air Cleaner Top No letters..RARE..If you do your own research, you can Google 1968 Shelby Original Air Cleaner and find a place that says NVSAAC Air cleaners and you will find the information..I included a picture of that web site on the last picture..Original Air Cleaner Tops like mine have a rectangular casting impression on the top of the air cleaner..please look at pictures #1,3,4,14.. On the bottom of the air cleaner lid, Originals air cleaner tops like mine, have circular casting marks..please look at pictures #6-#9..The fake or aftermarket Air Cleaner Tops, do not have the rectangular casting impression and the circular casting marks..I have not seen an Original Air Cleaner Top with no letters like mine anywere..