To answer you're axle question; It's a little more complex than that. You will need to figure out the backlash and pinion spacing. You may have to press the pinion bearing on and off a few times before you get it right. I usually start with the factory shims and go from there. I've only done 3-4 gear swaps, but they're all still holding up. Check out this site; it's for Toyota difs, but all the concepts are the same:
http://gearinstalls.com/