I wouldn't rebuild unless you had a actual reason to rebuild. If your motor is running fine now...just slap the mods on it and keep on trucking. These motors are a beast and mileage wouldn't scare me.
Do you have any pics of your header install? Either I'm an idiot or can't find any pics. Especially 04+ just trying to see how people worked the trans stick , the ac lines and what needed to be done with the radiator fan motor.