Well Angus Young's original SG is either from 1968 or 1971 (depending on the source you're reading), so those original pickups are going to be a little bit different from both the 490s and the '57 classics. In the Gibson USA Angus Young signature SG, there's a '57 classic in the neck position and an "Angus Young signature pickup" in the bridge. The Gibson Custom Angus Young signature SG has a pair of Seymour Duncan Pearly Gates pickups, though.
I forget the exact differences between the 490s and the '57s, but the general consensus is that the '57s are the better pickups. If it was me, though, I would go for something different entirely. My SG has Gibson P94s in it now, but I'm almost certainly going to swap those for some Bare Knuckle Pickups humbuckers of some sort. I'm just getting a little tired of the P90 sound in the SG.