I'd go back to the drawing board and start from scratch. I have found that I tend to bog down in old material, while starting anew lets me see things I had not noticed (or emphasized) before. This makes writing a lot more exciting for me -- and, hopefully, for the reader as well. Once I get going, I have found that writing new text actually takes less time than reworking old copy.

I never take an old book on the road with me when I'm about to write a new one.

For example, right now, I am writing a new book about the West Coast (among several projects). While I have already written several food, wine, and travel books about the West (plus several hundred newspaper and magazine stories), this new book is taking a totally different tack and, while it will touch on some of the "old" places, it will be as different from my previous write-ups as I can make it. I've already done a lot of historical and site research, delving much deeper than I have before. This is also making the project a lot of fun.

I would just clip out the facts as research already done, and then, as John suggested write from scratch. By the way, did you know you need to footnote yourself for any published work. This is another reason to just start over.