I have done a few sets of automobile heads (Chevy, Ford, and Chrysler) big block and small block and all I can say is that when porting aluminum it is very easy to take too much material, exactly as Pahrump said. When I blend the plenum on aluminum intakes and gasket and/or port match the intake ports, I generally use a cartridge roll and work very slowly, checking the material removal very often. You can probably do some good if you know how a port works and flow paths of the air. It was necessary for me to study and research for about 6 months before attempting my first set of heads. I also have a friend who professionally ports cylinder heads and intakes and has a flowbench to check results on. My first set was a set of small block chrysler smog deluxe heads. I was able to make 505hp and 517lb ft on the dyno after my port/polish job on my stroked 360. I invested a mere 100 hours in that set. Every set of heads I do are just a little better than the previous, so it just takes time, patients, and research. If you don't want to do all of this, then send it to a place like Duncan who already has it figured out. Just my 02.
Here is a chamber of a Big Block Chevy head casting 049 that I did.........
