forget about the ls7 unless you have tons of money, not just for the initial price of the motor - $15k (somewhere's in that price range) but also for the cost of converting the truck to a dry sump oil system

you will also need to convert to either an 80e or a t56 ( with extreme duty clutch)

a better option would be a ls2 stroker - 402 or a lq9 stroker - 408 built for lower compression to crank up the boost

a supercharger has more lowend tq and turbo has more hi-end hp however the turbo might be better for a dd 2wd because of the traction problems you will have

 

If you have the coin, build up a GMPP iron block for some turbos.