Andrew, hardened valve seats, which you don't need for your year model. Cheap head, try $2000 new from Cummins. Ouch.
Yours has them , and could be ported.
Add this and a cam, and watch your boost pressurs drop. Much more flow than stock. Then it's time for much more fuel.
For his year model, it makes better sense to use the head he did. I'm in the same boat, too.