I am not sure, I looked in the back of my lonestar, and there are small philips screws that hold the front trim piece on, and after that I think the grill is mounted on the baffle board. Remove the chassis and take a look, just go slow and un-plug every thing first.
PS If I were you I would try trading that custom orange cab for a black cab with the same specs. There has to be somebody out there looking for an orange cab. If you paint that cab black you are going to de-value it and like I said before I doubt it's going to come out looking very good.
