I don't think that particular part changed much over the years, and it's also relatively easy to figure out with SerialICE (www.serialice.com), since CAR is one of the first things to happen these days.

Since Intel wants everyone to use their code (preferably in binary form), I'm not sure how useful the BIOS Writer's Guide still is. Probably just a guide on how to integrate their code into whatever you're doing yourself.