Hey 73 sixpak, There are so many answers to your question that to save you time and answer your next questions...go to LATEMODEL RESTORATION SUPPLY and look up challenger rear end gear change.They show you how to install the 3.55 gears in your rear. The Diablo programmer does NOT recogonize the 3.64 ratios..axles are also different between the various housings,Getrag,Mettingen 210mm-215mm good luck--Cfan
