Wayne,
conversions are tough to figure. Standard typescript paper is 275 words per page, with a standard book 400 words per page. That way, a typical 100,000-word manuscript that's 364 pages in manuscript gets published as a 250-page book.
Adding imagery, larger format, wider margins for a book like yours changes everything. Your tome is 224,000 words, which is 815 old typescript pages for a book of 560 pages. Add images and you're up over 700 pages published. No wonder such books don't "move" in market terms. They can't even be lifted.
I can't translate typescript pages onto computer file pages because the fonts differ, there's basically single spacing, and then you're double spacing between enormous paragraphs. Writing in double-justified text also packs in more per page than would be the case if, as is conventional, you had single-justified it on the left margin. Not that it matters for editing purposes.
You are correct, the editing is necessary and painful. Also crucial in getting this into shape. The writing needs some work - always. It may be better and more efficient to knock out whole long blocks of text rather than think the cutting will come phrase by phrase. In my "Rough Meditations" manuscript, I submitted 110,000 words and we ended up just tossing the second half of the book and running the first half of it. For the Ross biography, by contrast, I wrote 105,000 words and that's what we ran - but the manuscript had 350 or so images and so the 400 page manuscript ended up getting published at 366 pages.
Warning. That book costs $85 (in 2001), full color, large format. Fine & Richardson's book on bunkers, 306 pages, medium size, partial color, also costs $85 (2005 prices). I can assure you no publisher is going to charge $105 for a Flynn book.
My advice is get a scissors. Not to stab the editor or yourselves, but to prepare for major cuts in the manuscript.