i just had the shock off my bike. the actual dimentions of the adjusting nuts are 60mm and 63mm. one is slightly bigger. and the notches are 5mm. the 68mm spanner should work fine. most tool shops only carry adjustable spanners anyway.
also, what we technically want is called a "hook spanner". cycle shops sometimes call em "c-spanner" or "shock spanner". this lexicon is probably only useful in the americas though. in british english, all wrenches are called spanners.
heres a hook spanner.
an adjustable hook spanner.
ive found this type of pliers can work just fine. the tip of the tool will easily grab hold of a notch in the nut. but if you're not carefull, you will scratch up the nuts.
all these tools only work while the shock is OFF the bike. theres just not much room with the shock installed. if you want to adjust without removing the shock, a hammer and center-punch, or a socket extender might work for ya.