My problem is after getting the new belt over the pulley on the transaxle the instructions say to pull belt forward and place over the upper pulley on the motor. The problem is that the pully for the mower belt that is at the bottom of the drive shaft is much larger diameter than the drive belt pulley and I do not have enough slack in the belt to get over the lower pulley.

Hi,
Bad directions there! Try instead putting it on the front first, but not completely. By this I mean to install it above the deck belt pulley, in between the two pulleys You should have enough slack to then mount it to the transaxle and then into the motion drive part of the double-stack beneath the engine.
Peace,
Clarke