Craftsman 42" T1800 247.203760 Problem Idler Pulleys Not Lining Up Level

Replaced the mower belt and did a visual check. Problem - the idler pulleys were not lining up. The right pulley is level, but left pulley is tilted, (5%-10% tilt). Removed the left idler pulley and re-installed. Used mower deck parts diagram to verify and ensure parts sequence correct. Belt Keeper-Shoulder Spacer-Idler Pulley-Cap-Nut & Bolt. But, the left pulley is still tilted.
 
Anyone who knows this model will understand that it's hellish difficult to remove/install this idler pulley. The bolt is inserted through from under the deck. Then there's almost zero space to find and hold the bolt in place from below with a 9/16th wrench, while tightening the top nut.
 
HELP! I've reached the end of my capabilities and just can't fathom how to level the left idler pulley. Will the belt keeper     hold the belt in place? Surely both idler pulleys ought to be lining up level?
 
Would be great to see a repair manual. Really hope that someone younger and wiser can offer me some direction.