It depens on the height of the spacer. If the spacer lift is 1.5" or less...then you can combine the 5100 series on the LOWER (1" ) setting, which works great. But 2" or more leveling kit can be use with the 5100 or HD but at stock ride height but a taller bumpstop is mandatory. Trying to combine a 2 0r 2.5" leveling kit and setting the bilsteins on any of the lift settings will result in probelms like this:
You can add a new UCA but the sway bar would either have to be removed or aftermarket endlinks made. This cant be stressed enough, LIFTS CANNOT BE COMBINED. unless you want to do some expensive testing.