Jeff
Itried running spacers on my 99 to accomodate 245's they were alum and they were not true (off by millimeters) and had a bad vibration problem. Try to use steel spacers if you can so they can bee machined to a uniformed thickness if you exp vibration.
05 3500 4X4 DRW Laramie 6 spd 325/610 4:10's
99 3500 4X4 DRW SLT ATS trans,edgeEZ,Auto Meter,AFE, loved that truck.