I was looking into putting one under my '73.. It seemed pretty easy at first, but then when we really started looking at things, it got a little more involved. I can't remember the exact length, but on mine, with the drum brakes from an earlier explorer I would have needed to use a spring relocation kit, or wheels with less back spacing. It was also almost three inches narrower. I was going to do away with my isolator axle perches and just use the ones that held the 8.8 to the leaf springs... it even had a sway bar.

The drive shaft also come out way on the side, and my fairly new custom exhaust would have needed to be moved. On top of that, the axles are retained with C-clips, which would be okay for mild applications.. If you can, grab the drive shaft for the rear u-joint which will have to be adapted to your drive shaft, which would have to be adjusted for length, balanced and re-yoked.

In the end, it was still going to be cheaper than any 8 3/4 axle I could find, because I couldn't find any... but then the guy at the shop told me about a '73 RR parts car for sale, and it had the 8 3/4 and a ton of other stuff I needed, so I went with that.

The A-body post has two really great links I posted, very helpful stuff.... It can be done, it just boils down to how much work you want to do to get it in there.