One thing you might look into is cross referencing the studs at the flaps. They should have a wheel stud book that gives the dimensions of the studs. You should be able to find 9/16" studs that have the same knurl (spined part) as the original 1/2" studs. It won't hurt if they are a few thousandths larger, they'll just fit tighter. You can install new studs easily your self using a nut and a stack of washers. You use the nut to pull the stud in with the threads, the washers act as a spacer and a thrust surface. There is also a tool available for about $35, but for a one time use the nut/washer deal will be fine. I did the same thing on my 3200 to change from 7/16" studs to 1/2" studs.
