Keith,
If you haven't gotten your carb yet, get the Holley 390 CFM. Holley has this aftermarket stuff down to a science. The carb comes with a DVD that is PACKED with useful info on understanding your carb and goes into great detail about re-jetting.
They spell out in a very simple manner how to determine the correct jets and how to change them. A complete set of jets will set you back about $50 so you'll be able to dial in exactly what you need.
My truck is about a year from being streetable so I can't tell you any first hand experience but I can tell you that determining the correct jetting and installing them isn't high on my list of "anxiety inducing" what-ifs list.
