I know it's Iron Man, but WHICH Iron Man?
 

So I've got this Iron Man. Pretty sure he's from Iron Man (I favor this because there's an Iron Monger, too) or Iron Man 2 releases.

6" figure
hands are replaceable (not sure where "human" hands are)
shoulder bits and mask (but NOT full helmet) come off

And the arc reactor.

He looks a whole lot like the Mark III or Mark IV, but the arc reactor comes out.

At least I presume this is the arc reactor for this figure, there are only 2 other Iron Man figs in the house and they have non-removable arc reactors.

Thing is, the arc reactor won't go in - it's too big.. I'm hoping by identifying the figure definitively I can figure out why. Is it the wrong bit? (if so, where the heck did I get this bit?) Am I missing some other bit that grabs it?