With Gallen's workrate, yes Prop is his position, but he may stay in middle third of the field, thats why the purpose of signing Andrew Ryan as the other prop for 2012 would be benefical, both great workrates, and big minutes, it would enable that between them they would take 3 hitups per set of 6.
Then we could use both the running forwards out wide and the backs, keeps Gallen away from the backs, but he can still use his offload