Help with 2500 Hd wheels

[deadshort52]

I am going to use some 2500 HD aluminum wheels on my C20 camper special. I thought I had this all figured out but I ran into an issue. My rear axle protrudes out to far to allow the use of the shallow factory center caps so I obtained two dually deep style center caps. Now the problem is that the dually caps are to big around at the base to mate up with the rim properly. in other words the cap doesn't quite reach the lug nuts so I cant anchor it. What do I need to do? is there another cap that I need to be looking for? Should I be looking at cutting down the caps? Longer wheel studs??? Please help.

Here are a few pictures to help clarify things.