I see that Auburn Gear makes two differentials for the 8 1/4 - the 27 spline AG 546072 for 68-96 and the 29 spline AG 546074 for 97-present. I'm planning to have custom 29 spline axles cut, so is there any other reason why the 546074 wouldn't work in the 72 housing? I also found this - "IMPORTANT: Chrysler 8-1/4 applications require modification to the axle housing as shown to provide clearance for the differential case. Clean housing after grinding." - from here - auburngeardiffs.com/product/546074/ But the site doesn't actually show what needs to be done, so I have no idea what they're talking about.