So,

I have a 2007 JK 2DR with a Smittybilt bumper and XRC8000 winch combo. The lift I am looking at is the Rubicon Exp 3 1/2" standard coil kit. As far as I know, they don't offer an HD front spring set. How much spacer should I use to level the front out? 1/2"? 3/4"?

 

Why not get the lift installed and go from there and avoid having/getting too much in the front? Its a snap to install spacers, so just eye it post lift and then pick the amount you need.... I mean, that's what I would do.... you really don't know how much the lift will truely yield until its on...

 

This is true. Chances are, the new springs will have a higher spring rate anyway, and not sag as much under the weight of the gear.

 

You may want to give Rubicon Express a quick call and just check to see if the front coils already have "leveling" built into their lift height. My Teraflex springs were already higher in the front to not only lift the vehicle but also correct the sloping factory rake.