I just did this same replacement 2 days ago. I used an open ended 11m, IIRC, with a 14" cheater and a very light pressure. The bolt backs under the WP pulley and is tight, but doable.
Good Luck,

__________________
Gary
Experience is something you get, Just after you needed it....
'99 E300 295K, '83 300D 220K, '75 240D 185K sold
'80 MCI Bus Conv DD 6V92TA, w/4 cyl. Kubota diesel GenSet 12.5KW