Neat idea, I think before I spent too much time on it I'd get the dimensions on the 4.0 to make sure it would even fit vertically. 4.0 only translates to 244 cubic inches, so its not all that much bigger than a 225.
If it can fit, then it'd be a pretty cool set up. Only thing will be that you'll be fabricating all of your parts- engine mounts, transmission mounts, etc. There won't be any vehicle specific parts for you, so even the aftermarket 4.0 stuff may not fit because its in an A-body and not a jeep.
There are a decent amount of turbocharged /6's out there already, so lots of info on how to do that.
Really just comes down to what you want to take on. Turbocharging and fuel injection on a /6 has been done, you'd be adapting aftermarket stuff onto the /6. Putting a 4.0 Jeep 6 cylinder into an A-body would pretty much put you out on your own, with the possibility of needing some pretty serious fabrication work.
