The best advice is to have your Source heads CNC ported by someone like Modern Cylinder Head. You'll have well over 600 hp with very minimal effort.
I've done a little hand porting on my Stealths. The seat and throat were a little mismatched and I cleaned that up. Also, the casting at the pinch-point was very wavy/lumpy. I smoothed that out which opened up the pinch point about 0.125" with plenty of material to go. Plus I smoothed everything else out without actually reshaping it too much.
Hopefully that will make a solid difference. Certainly not as good as cnc porting, but a good chunk in that direction.
