How difficult is it to install a posi diff in a stock (except for 3.73's) rearend? I picked one up for cheap and was wondering. If too much hassle, may just sell it.

It's not a do-it-yourself job, unless you happen to have access to a shop that has all of the special tools.

You also have to know if it is a 2-series or 3-series carrier, whether your gears are for a 2-series or 3-series carrier, and if the posi is for 26 or 28 spline axles.

If you like your gears, get a PowerTrax unit. You'll have to specify 26 or 28 spline axles, but other than that, it is a do-it-yourself job with basic hand tools and jacks & stands.

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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R. 2.73 unlimited slip. Cat-back from '91 GTA, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LB9 w/ZZ3 cam, TBD heads, exhaust, paint, etc.).
57 Bel Air, my 1st car. 0.030 over 396, Weiand Action+, Edelbrock 1901 Q-Jet, Jacobs Omnipack, 1-3/4" headers, TH400 w/TCI Sat Night Special conv & shift kit, 3.08 10-bolt, AMSOIL syn lubes bumper-to-bumper. Best 15.1 @ 5800' Bandimere. Daily driver while Camaro was being put together.

Just checked. 2 series carrier and 28-spline axles.