I used Infinity 6000cs 6" seperates up front and Inifinity 40002i 4" in rear. Did this because no modifications were necessary not even spacers.

Edit:
Ok correction to the above. Just called the installer to confirm even though he said he didn't use spacers for the front separates. He DID, just not ones I had to pay for. Being the enterprising young man he is he just used the Infinity speaker grille. Popped out the mesh, inverted the plastic and viola spacer. Sorry for the previous incorrect info.