I was the same as you dgc33, I didn't see how what Hughes told me was going to work. I asked Hughes specifically how they were able to do this with their retainers. I was told as you said that the relative position of the locks were the same but that mopar had engineered extra material on the underside of the retainer that was unecessary and that their retainers were reengineeered to do away with that extra material. They had redesigned the retainers to allow for an extra .125 of lift from the camshaft and that they were running camshafts in excess of .600 with these retainers. The second time I called and spoke to a different guy I was told that there was no clearance issue on the magnums in terms of putting a camshaft in there with lift over .525!!! . I just went out and measured the set up. I gutted a hydraulic lifter and used an adjustable push rod and set every thing up. With the 512 lift cam I still have almost .040 from the point of highest lift to the retainer hitting the top of the valve guide seal. I have stock thickness head gaskets on it and the heads were milled just enough to clean them up(a few thousandths). So in my situation I feel very safe at .512. At this point I'm not sure what to believe but I'm glad for this thread because I now know for sure that I don't have any clearance problems.