I dont run a cv on the front of my truck with duals as it is a pretty decent angle as to not need one.  I do run a cv on the rear beings I have a flat belly, even with the extra wheelbase I have over you it is still a bad angle, so it needed a cv to lessen the vibes.  On ShawnB's truck we found that if you are not going to flat belly your rig, and if you are going to keep the stock crossmember you should leave the cv in the front as youll need it to clear the crossmember.  In the rear just use the rear portion of your driveline as a core on a lengthened one for the truck.  You should be just fine without the cv in the rear, he has no vibes with duals in his truck.