Check out Lee Valley's book selection.
http://www.leevalley.com/wood/page.aspx?c=2&cat=1&p=46096&ap=1
Particularly the reprints of older books. A lot of 1860s to 1920s stuff, particularly things like windmills for pumps, over and undershot water wheels, etc. If he's handy, he can adapt those basic designs to other things.