I would find a full stock for it myself, that stock looks kinda short to me. Plus if you go with a half-stock you will have to put a under-rib on it. Also a full stock just looks better IMHO. Half stock rifles look uncompleted to me, IMHO again.
Go to Knob Mountain Muzzleloaders and check out the Hawken stocks he has, I would go with either Freds Full stock Hawken or the TH Hawken full stock myself. But from what folks say, its hard to do a Hawken "Correctly" if your a beginner. Oh yea, use the steel parts you have.