I was also going to suggest a Forstner bit in your drill press. Put some padding on the back of the guitar body so it won't get scratched, and use a couple Quick Grip clamps to hold it to the drill press base. You'll probably be able to purchase just 1 bit that's the same radius as the corner contours of the existing routes, then clean up the edges with a chisel. Just don't forget to set the stop on your drill press to the correct depth.
You could also rent a router at any tool rental place, and use a bit with a bearing that's the same size as the bit, as was suggested, (with that bearing bit, you don't need a template) and again, buy one that's the same size radius as the existing contours, whichever one is the smallest. Whichever "route" you go, if you have no or limited experience doing this sort of thing, I'd suggest practicing on some scrap wood first.
