The manual shows a large bar wrench that fits over a cam lobe, but it is used to hold the cam while tightening the sprocket bolt.
You could also try a pair of large vice-grips on the front of the cam and tapping/bashing them with a hammer.
But I really don't think you'll hurt anything if you undo the towers.
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe