8.75 Rear Gear Change Question

Sgt Lee, just so you know limited slip is a term indicating that the differential is a locking type that just slips a little when you turn corners. When you turn a corner the inside wheels travels less distance than the outside wheel so you have to have some sort of device that allows the wheels to turn at different speeds (a limited slip differential). The other type of differential is the open differential that has no locking device to lock the wheels together when your going straight. They generally pull mostly on one wheel. A lot of guys call them a "one wheel peel" because when you do a burn out it only spins one wheel

Positraction is the term Chevrolet called their limited slip unit. Sure grip is the term Mopar called their limited slip unit. It's really just a matter of terms but when said wrong can rile some guys, LOL...

Changing gears isn't for the faint of heart. They have to be set up within .001~.002" of an inch or the wear pattern won't be right and they may howl like a banshee and/or wear out real fast. It takes special tools and know how to install new gears. If you have an open differential (sounds like you do) you'll also need a sure grip (limited slip) unit. You'll want it installed at the same time as the gears. Since you have no experience in setting up gears it'd be in your best interest to buy one already done from a professional. I have seen them sell on the for sale forum for $400-800 depending on the gear ratio, type of sure grip (cone type or clutch type), and the age of parts.

Just so you know, any Mopar 8-3/4 case (741, 742, or 489) will bolt into your rearend housing which is great but there were a few different u-joint sizes used in the different body styles. It's a 99% chance yours is the small 7260 U-joint because that's what was used in nearly every A-body. Make sure you verify that when buying a rearend. Sucks when you buy something and have to modify things to make it work.