I took some ideas from bumpers I had seen (I linked to a couple of them in the pictures), but I mainly just designed as I went.
Personally I have never understood why people use Autocad so much unless they are using a CNC plasma table or something like that to cut the metal out. The looks can only deviate so much from what all the other XJ bumpers look like and we are not dealing with very small clearances. Hammer to fit usually works just fine.