OC, I don't use the internet much for decoding. I have several reference materials/books here at home. My GM stuff is packed up right now, but I used Mark Allen's I6 book
http://www.msa-1.com/ and Leo Santucci's books
http://www.barnesandnoble.com/w/chev...cci/1119499257 for your questions. There are several good sources on the net, Stovebolt.com
http://www.stovebolt.com/ Nasty z,
http://www.nastyz28.com/decode.php Also a google search using the casting number you want to find info on, will usually turn up a discussion or two on a forum somewhere, of someone asking about it. I-6 info is the hardest to find on the net.