Rear end Swap

I'm doing the same with my Sport. If you're not worried about keeping the car "pure" the common thing seems to be the Ford 8.8 from a 95-99 Explorer. For around ~$200 you can get a 31 spline axle with limited slip and disk brakes. It's a simple swap, you just shorten the longer side to match the short one and put new spring perches on. I'm actually keeping mine at the stock length so it'll be even easier. The alternative is of course the 8 3/4 but I haven't found an A body one for less than $800.