Thanks for sharing your parts book with us
As far as I know nothing changed. Four or 5 other members contacted me saying 52" was correct,and in many old threads others had said 52" as well. I've also had a couple folks in my wanted to buy post for the driveshaft say and show with photos that your book is correct. One member has both 67 and 74 dart driveshafts removed from 904 trans cars with 8 3/4" rear ends..same thing 52" so it would appear your 67 book is right and applies to my 68 dart and later models
Maybe someone here with a 68 parts book will chime in. Youre right about measuring twice,but hopefully im not cutting my driveshaft though. The goal is to buy one that's factory made and correct and not mess with mine.