You can always customize your paint and interior colors if you're doing a factory order.
I think the 500hp ISX 12 on the K2 is a cut-down model of the standard 600hp ISX, which is 15 liter (well, 14.7, I think). So it won't be an ECM change to get to 600hp.
2008 King Aire 4562, Spartan K3(GT) w/ Cummins ISX 600
2014 Jeep Grand Cherokee Overland 5.7L V8 Hemi w/ Blue Ox Aventa LX Tow Bar and baseplate, SMI Air Force One brake