The shell is pretty easy, the only 2 areas you need to touch are the tunnel (drivers side at front) which can be done with a hammer or by welding in a section of a 4x4 (or make something up). The other area is the front chassis legs....the chassis legs foul on the driveshafts if you ever hit full compression on a front shock, so they need notching out. Ford did this on all the 4x4 shells so just have a look at one.

Some people will tell you that you can get away without notching the chassis legs, thats fine I suppose as the risk of bottoming out is low. But if you want to lower the car a lot or hit a speed bump a bit too hard you dont want to run the risk IMO, ford saw it fit to do the mod to the chassis legs so In my book its a required mod.

Cheers
Dan