I've got a 97 F150 with the 4.6. I've used both 5w30 and 5w20 as Ford now recommends the 5W20 for some of the previous models. I'm not sure what some of the numbers mean either. But if you're concerned about warranty issues, I'd stick with the Motorcraft 5W20.
I feel safe using either. When I use 5W30, I use Mobil1 and if it's 5W20, it's Motorcraft, Pennzoil, or Chevron Supreme. When using those I change at 3,000. If using Mobil1 I extend to 5,000.
John