hey man from experience dont evr ever go with kits like that, if you want to get a twin engine truck then get that, you will be better off, conversions and things like that always break something or require modification which can ruin the truck if you want to switch back later, its cool and all but it will definately cause problems, your better off going to just go get a really powerful single engine for it and a on of steel parts for the driveline!!!
PM me if you decide to go with this method and i can give you a few suggestions on what you should do, and what engine, or engines you should go with