Porting is going to be the best power increase for the money IMO. I had Wildcard Racing port my dune bike and I love it.
One thing to consider before porting, I have heard the T-6's don't respond well to a ported motor. Might be something to looking into, I'm no T-6 expert though. I've always ran CPI.
I wouldn't bother with bigger carbs until you do some porting. Also, you can run stock carbs just fine on a ported motor as well. I've seen motors run up to about 65-70HP with stock carbs.