Here is how you set up the belt and check for alignment. The straight edge is held tight against the clutch drum and intersects the center of the motor pulley. My dad measured the distance from the back edge of the motor pulley and zeroed out the caliper.
Here he is measuring the distance in the same spot on the front of the pulley. They have to be within .020 thousandths of an inch. It is also worth while to pull the spark plugs and kick the system through a dozen times and double check that everything is tracking straight and the belt isn't rubbing anywhere. Once this is set up, you never have to mess with you motor and transmission settings again!