OK, in this scenario, Galactus finds the Earth all of those years ago instead of Zenn La. Everything transpires nearly the same except Galactus prepares for all of Earth's defenders by sending hundreds of Punisher robots to distract them while he prepares to feed on the Earth.
Danny Rand (Iron Fist) of the 70's get's to the site that Galactus is setting up his tech for absorption, and makes a deal with Galactus that he would sacrifice himself and become his Herald. Galactus accepts, and turns him into the Silver Surfer. Danny uses his powers differently than Norrin Rad does though, and is known to transform his board into swords, and other objects while in combat.
Years Later, while Danny scours the cosmos in search of a suitable planet, he is pulled into a wormhole, and appears above Apokalips which is ruled by Darkseid.
He investigates and finds himself smack dab in a battle with the planets master.
Iron Surfer wouldn't have the scientific understanding of Norrin to make the best use of exotic potentials latent in the PC. So I see him as more direct and physical.
Norrin would probably have found a way to free the minds of all the inhabitants and cleanse them of Darkseid's corruption.
Rand would just punch Darkseid into a burger and then layout a table for Galactus to lunch on Apokalips.