Hi Justin,
This site (
http://corvetteactioncenter.com/tech/rpo/8496rpo.html ) listed all but one RPO for my '85 (66M) so it seems to be fairly complete. The only source I have found that is better is the actual GM Corvette Parts Manual (had the mysterious 66M). I have one for '84 - '88 in paper that I would be happy to look up codes for you in. FYI, the C4 parts manual CD on eBay for $22.80 is very good and covers the entire 84-96 C4 series. Have used it extensively to track down parts and determine interchangability. It is a Acrobat PDF version of the deal fiche with page number corresponding to the fiche grid coordinates so you can navigate using the original fiche indexing scheme.
Rob