I just got a 2004 Heritage regular cab, 6'6" bed. I'm looking for used bed covers and I find some that say they will fit a 2004 F150, but NOT a 2004 F150 Heritage.
My understanding is the 04 Heritage is the same as a 2003 model. So, can I look at covers designed for 2003 models?

 

That is correct, your truck has the same body style as the 97-03 model f150. In fact, you would be better off in the 97-03 forum, as your truck is essentially a late 03 model