If by chance you can locate a cracked or broken head of the same # as the ones you plan to port out, have the head cut directly through the ports so you can see what the port looks like from the inside. This will let you know where your water jackets are, and help you prevent getting into a thin area where 1/16th of an inch of grinding could ruin the head. Studying these cut ups will also give you a better chance to analyze how the intake and exhaust runners are constructed, and give you a better idea of how the flow goes.
You are correct about fuel air mixture velocities, and this holds true regardless of the RPM design of the engine. The trick is to maximize the velocities and volume of flow to correspond with your desired RPM range.
Just remember that a little of grinding will help a lot but a lot of grinding isnt always gooder.