Wow, that 5.0 ratio would turn her Jeep into an awesome rock crawler. What kind of offroading are you into? What size tire and lift?
There is a bit of work ahead of you, the Atlas is not a pure bolt-in job. I'd probably go to the Pirate4x4 forum and do a search as there are a lot of threads there having to do with installing an Atlas.
Be sure you really want/need that 5:1 ratio, that's a pretty steep-low ratio for most needs and it'd be a bad ratio choice if you are into anything like mud where wheel speed is needed at times. But for rock crawling, it'd be ideal. Good luck with your installation, that's the one remaining major mod I am dreaming of for my TJ.