My 10 hp 30” Craftsman is basically the same as the Murray.
I have found the best way to replace the 37 x 65 motion drive belt is this:
# With the pedal disengaged and the front wheels turned to the right, remove the mower deck and the belt. The manual explains how this is done.
# Engage the clutch and set the brake. Remove the four nuts from the 1/2” bolts that fasten the transaxle to the mower, but don’t remove the bolts. Remove the nut and the short carriage bolt from the bracket on the rear of the mower.
# Raise the rear of the mower about 2 or 3 inches with a floor jack, while observing the four axle bolts. They should stay in the holes of the axle.
# Route the motion belt as the manual states, starting from the stack pulley, and work it to the drive pulley. At least one belt guide will need to be loosened during this procedure.
# Carefully feel the drive pulley, there will now be enough space to slip the motion belt over it, making sure it is routed correctly.
# Reverse the procedure. It takes me about 2 hours to do this.