Paid 2 bucks for this at a garage sale today. Has 110 pages of 80's rpo codes/info as well as cross referencing of part numbers for new vs reman parts and lots of other info thats probably useless now. If you give me a 4 digit wire harness number from the 80's I can now give you the 8 digit GM part number for it LOL. Same with seat belt tag numbers. The little white book I found in a parts car, thought it had lots of RPO info till I found the red one. Red one even has the GNX rpo in it. So any of you searching for mystery rpo stuff, maybe I can help?