magnum cam extension from hughes?

Sorry to hijack..., but, I need some help with this one-I bought these same parts from Hughes-the snout extender and the moly coated eccentric and can't get them to play nice. I'm using a '98 5.2 Magnum, stock cam, and a autozone replacement timing set (#73089), and no matter how I configure the pieces, I can't get it to secure correctly. The instructions say to machine off 0.100" unless you offset the keyway in the retainer, but if I do that, the timing gear moves back and forth on the cam, and it's not like I have a machinist at my beckon call. The biggest problem I think I have is with the timing gear, but I can't compare it to the old one as it was lost or thrown away during a move when I was deployed last year, so I really have no idea what's wrong with what I'm doing.