Not hard, just needs care, like most things. If you get one of these sockets it'll be a big help. The nuts and lock tab are unusual in that the tab is not keyed to the stem, allowing both nuts to turn (tighten) more when locking them up. Use a maker pen on the lower nut to ensure it does not turn further as you tighten the upper one, after you've got it adjusted correctly.
http://www.ebay.com.au/itm/Kawasaki-Ninja-ZX-14-Concours-1400-Steering-Stem-Nut-Socket-Headrace-Socket-/110996870200?pt=LH_DefaultDomain_3&hash=item19d7edd438