Copying Port design for CNC porting

dont have any experience with that but i would gues it could be done the same way as exhaust companys does it, you use a mockup set of pipes that you measure with the help of a sensor on a measuring table that puts all the cordinats into the computer that then runs a cnc bending machine,but it may take alot more time to measure out a complete set of cylinderheadports since it would require alot more spots to measure before having the cnc mill do its work. also it may be a problem with inconsisten castings since not all heads are the same and will tolerate as much metal being taken out in some spots