[SkinnyG]

Hmmmm.... that's disappointing. Powertrax sell a "helical diff" too, but also 3.73+.

You're not going to be happy with a "drop in locker", also known as a "Lunchbox Locker." It's a mini Detroit Locker "ratcheting" differential that replaces your differential gears. Noisy and a bit unpredictable on/off throttle. I recommend Lockers for dirt, drift, or drag; not street. Easy to install, yes. But you might not love it.

An auburn diff uses cones, which is similar to later factory limited slips. They are relatively smooth, but not rebuildable.

Your basic clutch-type posi might be your best bet, given the options. It will work fine, and I'm sure you will be much happier with it than the locker.

As for install, you will need a press to put new carrier bearings on. You don't have to touch the pinion at all, but try the factory carrier shims and then check the backlash with a dial indicator, then visit your local rear-end shop for some different shims to get good pre-load but the correct backlash. Or just take it to a shop you trust and pay the man (much safer).