I also converted to a 5.3, but made my own tank. Converting an original tank is fairly straight forward if you have some fabricating capabilities. My best advice is to use as much OEM stuff as possible because it will be much easier getting parts later on if a problem should arise. I used a factory 2003 pump and assembly and have no regrets. In fact, I've used these assemblies on a few builds. They are cheap and are self contained including fuel sender, roll over valve and return line. Another bonus is that the assembly will adjust to different depth tanks so it's an easy install. While you're at it, cut an access hole in your floor so that you won't need to drop the tank for any future pump servicing. One last thing I would recommend is plastic (nylon) fuel lines front to back. Once you use these, you will never go back to the old steel lines.
