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Anyone thought of Micheal Pitt from Boardwalk Empire. Not quite physically imposing as the other suggestions, but he is still pretty scary (alla funny games).
I think Chistian Kane and Joe Bernthal would probalby play more in there 40's than 30's
Personally I'd be against Jason Mamoa I find him to be wooden and/or cheesy (see Stargate Atlantis). He does much better when there is just action or he speaks in a made up language (see Game of Thrones).
Ryan hurst is a good choice also