the back plate touches what?...I had a 3.3 in mine a while back now it has a BB .28 in it.I can't remember how it was mounted. It might have been on different mounts.The BB mounts I have on it now I had to re drill the chassis.The 3.3 was faster than The BB.I'll look and see if I can figure it out again.PM me if I forget to get back here.