89 limited slip Ford 8.8 IRS swap help

Good read.:study: Thanks for the links. I'm definitely going to buy that book you noted in your article. I'm going to head to the drawing board ASAP. A few questions though. Why couldn't the stock cage mounts be modified to mount to the frame rails under the car? Seems like that would solve a lot of your structural issues? Did it incorrectly distribute the weight that way or was it just a clearance thing? Also what if the frame rails were cut and fabbed differently? I'm ok with the stock length of the half-shafts because I plan on squaring the car up and extending the front end out a few inches as well for a larger track width(looking at some wide body ideas for body work). What was your total cost developing the prototype?

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.