The Chevrolet caprice and Corvette have been using them for years.....
The only kit I have found for the 4.0 is a universal kit requiring you to bolt on a motor on a bracket. I have never liked that idea. and the electric motor is going to draw close to 20 amps and that Will load down the Alternator, causing an electrical drag..
Underdog a sponsor here sells the under drive Crank pulley and the under drive W/P pulley. You have to have the crank pulley to use the W/P pulley.
I have had them on my truck for about 6 months and thats the way I would recommend going..
Also throw on an electric fan and your set.....