Doing a dovetail on the besides is definitely one of those things you don't want to mess up.
A Sawzall with a very very fine metal blade works well. I would not go less than a 18t. More teeth, the cleaner the cut.
Before cutting away, use some masking tape, layering it a few times (to keep from scratching), where your cutting, and then you can draw your preferred cut line onto the tape using a ruler or straight edge.
Be sure to check out the newly released SVC Baja Rear Bumper! Clean design that retains oem reverse sensors, plate lights, spare tire lock. And also moves the hitch up and behind the license plate (which flips up). And space for a couple rigid dually (or similar) reverse/running lights.
Shoot me a pm for a quote if your interested!