Once you lay the subframe under your car, you'll start to see why it won't work. In my case I didn't want to cut up my car, so I made the frame to fit the car. If you were hell bent on using the Ford subframe, you'd probably end up doing a complete back half. IE: Cutting the bottom of the car out and building a new structure and sheetmetal. You'll also lose your gas tank and have to run a fuel cell.
If you're going to a wide track, I think you're better off going with one of the full chassis kits that a couple vendors offer. Even if it's not for a Mopar. Like this:
http://www.artmorrison.com/ or
http://roadstershop.com/
We're talking over the internet here, so I don't know you or your skills. But what you're getting into is some serious money and time if you go this route.
The cost for my rear end I'm not sure of. It wasn't a ton, but I did most all the work and pulled favors on the stuff I couldn't do.
On my Dart, I started upgrading the stock parts first and got it handling pretty good. I also wanted to do something different and that's why I did the IRS. The results were okay, but to really make it good it needed more refinement. I didn't really have the desire at that point to tear the car apart yet again.
I'm rambling now, but bottom line is you need to take a sober look at this. You need to have the money, time and patience to see this through. If I were in your shoes, I'd upgrade the stock suspension so the car isn't down for long periods of time. This keeps your enthusiasm going and the car on the road.
