Check out my build thread, I cut holes in my front bumper and did them like a 70 Road Runner. I wanted driving lights in the bumper. There isnt any reason wht you cant make a pattern for the holes, very carefully mark it out, and use something as simple as a jig saw with a steel blade on it to cut it out. What I suggest is that you transfer the pattern to the bumper, then cut well inside the lines. This way, if you get a little shakey while cutting, you still have some room to fix it.
After you have them cut out. Then use either a die grinder, electric grinder, or even a file and clean up the holes til' the lights fit like you want them too.
Im nopt too familiar with the bumper brackets and how much room you have to change bulbs. Im assuming, that in the worst case scenerio, you could fabricate a "low profile" back housing for your light fixture. Maybe that would be a good idea too. Otherwise, you may have to cut out the area behind the lights and fabricate a new "recessed area" for the original light housings to have room to fit back there.
Dunno, if this helps but......
Also, do like I did, I found a second bumper, so I wasnt so scared to cut one up! It doesnt have to be a perfect bumper. Believe it or not they are easy to straigten with a decent sized hammer and a 4X4 as a dolly! LOL
