The "leveling" kit is suppose to level the truck. So technically you dont need rear blocks. It will make the truck look level. All the leveling kits are the same. All they give you is keys so any will do. Check the site vendors. Im sure theyll hook you up :rockin
If you want the best, you should look at the Cognito Upper Control Arm Kit, it allows you to level the truck w/o a harsh ride. It's a bit spendy, but worth it in the end. Cognito 01-08 GM HD leveling Kit
cognito is awesome!! If you are close to needing upper balljoints...get them. I am kicking myself for not doing it sooner. Getting better/longer shocks help out a lot. I didnt change out my keys..just cranked the ones I had.