Considering that Iwo Jima wasn't attacked until 2/45, it is pretty reasonable to assume that type 2-3 rear sights were used there. My 3/44 and 9/44 carbines both came from the factory with them. Additionally, the Iwo Jima attack force was assembled in Hawaii, trained there and consisted of many raw recruits straight from the states. Probably hundreds of brand new carbines came with them.
The guy watching the B29 ditch looks like an Army troop to me. I vote for Tinian for the photo.