[mickmate]

I wouldn't recommend drilling from the inside out even if you had room to.
You can start with a drill on the outside perpendicular to the body. Once it is through it can be carefully strightened to the hole to make more of an oval shape. I used a die grinder similar to a Dremel tool. If you want a printout of the oval shape I have one I can send you. You can just measure it easily inside the groove with calipers and having made sure the hole is centered to the bracket behind it and just reproduce the oval shape.
Another method is a hole saw with a pilot to fit your brackets either over or instead of the drill. As pointed out always mask it well and use sharp tools from sandpaper to drills so it cuts not rubs, chips and burns.