I could have had it easy - having a RHD car means I could get the bracket from a LHD car and put it on the other side...
I didn't - I ordered two repro brackets from Mac's, one each side. That way they are the right shape for each side, and they are both the same.
I did as mentioned above, and made sure the first hole is correct. I measured from some specific body joins/points, to give me some reference points and measured from them to give me the exact point. You just need to make sure it looks right on the car, not compared to the back ground.
I was very hesitant of drilling the hole, but I'm glad I did it now! The more people seem the lights, the better!