If you think the 03/04 6.0 and the 05+ 6.0 are similar, you'd be way wrong. They changed a LOT of stuff on the motor alone, not to mention the chassis stuff. You'd be hard pressed to find the same parts on an 03 motor as you would an 07 motor.
500hp daily driver is easy actually fora 6.0. 600 is harder, you will need compounds for sure.
What are your plans for the truck and how much are you looking to spend?
7.3 and 6.0 have the same fuel system? Hardly. Sure they're both HUEI, but they're not the same. You wont need big oil on a 6.0. Big oil from a 7.3 wouldn't even run stock 6.0 injectors.