If all you want is posi-trac then why not just buy a new limited slip diff and install it (or have it installed) in your rearend? Or buy 59 wagon man's. Either option would be immeasurably easier than finding a nearly 60 year old posi-trac differential in a junkyard in working condition. http://www.jegs.com/i/Eaton/362/19686-010/10002/-1
A '55 to '64 rear end from a junkyard can be guaranteed to have done its share of burnouts, meaning you might have to either do adjustments or end up replacing bearings, gears or both, hoping that at least available gears of OEM quality are still available. If that Eaton set-up isn't some 3rd World product, that would be the quickest and best way out, if that kind of money is expendable. All that'll be left to deal with, after that, is the disc brake conversion and the new plumbing to work them properly.
OK guys and dolls, I've done my research and decided to go with the 68 69 Camaro 12 bolt with disc brakes. It's the right width, has disc brakes and posi traction. Gonna start looking for one with 3.31 or 3.55 gears. I'm not in a rush, so when I find the right one at the right price, I'll get it. Time is on my side. Thanks for all the advice. BTW, Sarge is ready for the paint shop. While in the paint shop the seats and door panels will be in the upholstery shop. Getting close!
Good choice, stick with Chevrolet parts. Sometimes it's cheaper just to buy the whole car and strip your needed parts. Don't know why everyone wants to spend your money on a 9"? I put a posi unit in my '65 Impalas factory 10 bolt rear end. From what I've read if your not running 500 hp with slicks you'll never break it. I honestly can't say I've heard of a street car breaking a rear end not that it doesn't happen. I've broken U joints and Saginaw transmissions but not rear ends. Never had a 12 bolt.