I'm not too knowledgeable on DK tanking, but a little more health doesn't hurt. I've seen them in action and their threat generation is pretty awesome. You should try to replace the anvil with the essence of gossamer from the 2nd boss in heroic azjol'nerub. Also try getting the +40 stamina enchant for your wrist. Attack power is great and all, but your threat generation should be more than enough even without that anvil trink and AP enchant!
Also whenever you get a chance, enchant your shoulders with lesser pinnacle or greater pinnacle from sons of hodir. Finish off with an enchant on your gloves for expertise and add a belt buckle socket on your waist and put a stam gem in there.
All you really need for starting Naxx10 is 540 defense. You do need a bit more health (and new trinket and bracers), but that shouldn't be too hard to get. A couple of tips: Enchant your shoulders and gloves and never ever gem for parry.
The trinket from H AN is awesome, and you can find decent bracers in H OK, H CoS and H UP, or you can just buy the Valor ones.