I've been seaching throw a creap load of websites looking for a turbocharger with no succes. I have found a super dont want it on a 4.2. Anyone anywhere if you foundone say so!

 

If you want twins go with 2 T3's, if you want a single go with a T3/T4B. Just about everything else you do will have to be custom. Unfortunately nobody makes a turbo "kit" for the 4.2 that I know of.
There are a few 3.8 Mustang guys with turbo's and at least 2 of them I know are working on producing kits. I'm not sure if they'd fit in your trucks though