The only thing that might be an issue for you unless you can program plds, is that you might have to implemenet the encoder pld as discrete logic instead of using a pld. Other than that, it looks like a fun project!
AND, in fact, the link
http://www.datasheetarchive.com/preview/683956.html has a pdf wherein just such a circuit exists using a pair of d flipflops! This is for a quadrature encoder.