I bought a set of J&M C/C plates and am in the process of installing them. Only problem i'm having is, where does that rubber bushing go underneath the dust cover? Do I even reuse it?

 

The piece that you are referring to is the Bump Stop. You will need it again depending on the struts you are installing. It will go underneath the dust boot on your new struts with the factory dust boot going over it. There are directions to installing the CC Plates on Maximum Motorsports web site if you have any other questions. Bilstein Struts do not need it since they have built in Bump stops for the front, the Rear however work differently. Hope this helps.