jack hotrod up, front and back. find an alignment hole under the frame near the trans cross member and measure to the grease fitting on both lower ball joints. this should be real close to each other. take plumb bob and drop a line down from both front grease fittings and mark the garage floor. go to the rear axle as close to the braking plate as you can and drop the line down from the front of the axle on both sides and mark the floor. measure these marks diagonally. they should be real close to the same. if not you will need to move the shortest to match the longer one. the required distance will be added where the front spring hanger is bolted to the frame.