1) Do I need any spacers? I have some of the GMT400 dually front spacers (about 1/4" thick) that have the alignment pins ground off and can get another pair easy enough.
Not sure exactly what you mean by "spacer". None of the GMT400 Duallies I've ever service had any kind of spacer, other than the dual wheel adapter for the front. Are you actually talking about the plate that goes on the outside of the wheels? If so, those are not meant to be used as a spacer, as they have the seats for the lug nuts machined into them, along with a raised lip around each lug hole. That will not allow the wheel to fit flush to the hub, potentially causing poor lug torque and wheel loss.
