Can a rear end be converted to posi-track

Try putting in one of these:

http://www.lockright.com/

I put one in my Jeep and it works great! It works just like a Detroit Locker, but it's not as strong since it uses the existing differential housing. It replaces the spider gears with a locking system. When it locks in, it's 100% locked, so even if one wheel is completely off the ground, the other wheel will get power. It does clatter on the street when you make turns and can cause weird handling on snow and ice. I installed it myself in just a few hours.

www.northernautoparts.com has an aftermarket diff locker

How did that engine swap you were talking about go?