MY ADVICE:
first off...... you need to do A LOT of research. i've never done it myself (i plan on it in a year or so). it's a very precise process that can require some very expensive tools.
read all the articles in the tech library, check out youtube and other forums/sites. pirate4x4 has a good one
http://pirate4x4.com/tech/billavista/Gear_Setup/
i'd consult some of the member's on here before you do it as well.
secondly......i wouldnt even bother with the swap for a few reasons. that axle is weak and sinking $$$ into it isnt worth it. it would really suck if you spent all that $$$ regearing and then you blow up the diff or snap an axle shaft.
you could probably find a 31 spline 8.8 with 4.10 gears and get it installed for less than (or maybe a little more) it would cost to buy just the gears for the 7.5. or if you wanted to keep the 7.5, you could probably find one with 410's already in it too
it really depends on what tire size you're running and how hard you beat on it (giggity)