Yes to the backplate. I used one from a Zalmon 9500. Before I had 7C spread between cores. Now all cores have less than a 2C difference and are usually 1C apart. :) Conventional wisdom is don't lap the D-Tek Fuzion. It was designed with a bow on purpose and that helps provide lower temps. I've read a few reports from people that say lapping helped. That one is a coin toss. I'd use nozzles without lapping.
Edit: You don't have to make a back plate. You can always buy one of these...
http://www.petrastechshop.com/dfuprha.html