There's not very may books that reference the Montego, let alone dedicated to the Montego. But here's some that I have found. I've also included some good reference material on Ford engine building. I used these when building my 351W.
<<< 'Road Test' of the Mercury Comet & Cyclone. Technically nothing to do with the Montego, but there's lots of good info and pic's of the 69 Cyclone, starting on page 74.
<<< This is a good book. Goes over all new features for 69, positioning, tech data, accessories and optional items. These are avilable as a reporduction - I've never found an original copy. A must have!
<<< Good book which I used for referencing casting ID's. Has some good engine pictures and is split between big block and small block.
<<< Not my favorite, but has good info on building your engine for performance. I was looking for mild, this dips into the wild catagory. Covers small and big blocks.
<<< Lots and lots of part numbers for every aspect of your Ford engine, including cam's, carb's, and hard parts like engine and cylinder heads. Good reference material.
<<< More geared to late model small blocks. I did not like the assertion made in the book that all small blocks (289, 302, etc.) were Windsors... not true!