The carrier doesn't have to be replaced, just the spider gears inside the carrier! The spider gears are what the axles slide into. You can get a set of 31 spline spider gears for $130, but they are a pain to install them especially with the s-clip.

Also, I never used any specialty guages with my gears. I placed them on a table and matched them up with my eye. They were super close and the marking compound was perfect. The backlash was felt by hand and was awesome. For the crush collar I used an old method for torque(3ft breaker bar would just barely fall from 3'oclock to 6'oclock after torqued). For newbie's I reccomend having a shop do them because I have done so many I can do it with my eyes shut! I wouldn't reccomend my way unless you have done many and know all the tricks.