Toshi, you have done a great job on the P-61. I've always liked that ship since I built the Airfix kit back in the 60s and walked aroung a real one at the Air Force Museum back in 1970 when their larger aircraft and most f the jets were kept outside and quite accessable.
As for the radar, I would just paint the radome like on most aircraft, to me it just looks better. But then I would have even more left over spare parts in boxes. Another option would be to do what Shep Paine did in his diorama series for Monogram back in the 70s and give it a maintennance appearance with the radome off as well as other areas being worked on.