What are my Stock rearend Gears?????

[RPM427]

You do need to set up FMS gears, regardless of what someone tells you.

Basically you must preload the pinion bearings by tightening the pinion nut so that it requires 12-22 inch-pounds of pressure to turn the pinion with out the ring gear and carrier in. If you tighten it to much you need to get a new crush sleeve. You then will need to check for a proper mesh pattern and that will tell you if the pinion shim is correct. You need to shim the carrier so you have between .012-.015 of backlash checked with a dial indicator. If you just install your new gears without setting up a good mesh pattern, you will hear some whine, feel vibrations, or destroy your new set of gears.

If you don't care about bad vibrations, loud whinning sounds, or longevity, then try to install it yourself. My advice is to take it to a proffesional.