porting is always a good idea, but since you are using non-performace exhaust and an intake not much better than stock I doubut you will see the advantage. If you went w/ headers, RPM or S/D intake and 3.91's you'd see the difference. I ran 12.90's w/ stock 906's on mild 440. The valve job and angle cut will help, also if you plan on adding to the build later the porting will help. The problem is the cost. It's probably going to be cheaper just to buy the stealth heads in the long run. I mean you reach $800 pretty quick when you start grinding, plus it already has 2.14/1.81 valves. 906's have 2.08/1.74 valves. If this is a car you just want to beat around the street with I'd just stick with your fresh 906's.