I came across this, might be your answer.
"You'd test it the same as you would any other head. Flow it at 28" and see what kind of results you get. The airspeed in the ports on the running engine will be the same regardless of boost since the airspeed is a product of the ratio of bore area to port area and the piston speed of the engine. The boost is only a measure of the density of the input charge as it relates to atmospheric. The density of the air will have virtually no effect on how the port flows, if you have a troublesome head on the bench you will see the same problems on the running engine. I had a chance to discuss this topic with Ken Sperry at the PRI show a couple years ago and he said basically the same thing."