I recently came across the original build sheet for my 1970 El Camino. Does anyone know where I could get a document to find out what all the codes mean?? I know what all the RPO codes mean in section 107 like Z25 and L34. I would like to know what the specific section codes mean for the 123 sections. Like under the 55 Air Cleaner section it has "SS" and under the 68 Master Cylinder section has "CN" I'd love to know what all these mean.