Try dry fitting them first before you do any kind of mod work to them. I bought a nice set of couch mounts that didn't need a thing done, in fact they were better than the original SJ mounts. The couch mounts I am talking about though are my second set. The first set I bought I spent a lot of time on a mill trying to get them machined to the exact angle as the SJ mounts were because they did have a slightly sharper incline to them. I matched up the proper height needed, angles etc...only to have one snap in half on the bottom plate after a few rides. Before you decide to take material off of the bottoms, go back and check for a third time, you really don't want to put time into thinning the bottom plates down if you really don't have to.