I have an XD with drums that I am about to convert to E series diif the E series diff has a disc brake setup it will just need a good overhaul easier for me to leave the drums if they fit. I cant see why anyone would take the drums from an X series and put them onto an E series though. (im guessing thats why you are asking why) Already have front discs, drums at the back makes for better burnouts don't you reckon? Why did you do it?