What I have done is drill the spring pad with a new locating hole 1&3/16 to tho front of the hole which is centered in the spring pad your going to use. Double check this measurement as my memory isn't always right any more. I also add a second leaf[longest leaf without the eyes on it] to help prevent wrap up, and remove 1 or 2 shorter leaves. to prevent raising car. I have also cut a main leaf just behind the rear end and cut the eye off and mounted it under the main leaf to prevent wrap up. There may not be anything you want to use here but this is stuff I done before There were custom made springs. OLD SCHOOL 1 OL REDNECK
