I don't know what the intent of your use is but I have helped a few guys build 270's which were very good performers and did not use any big port head. If you really want a big port go with the 302 "D" shaped chamber. A flat top piston and .100" off the bottom of the head will give you more compression than doing the same to a "H" head.
It's been my experience to use a small port head(last small chamber) with a big port manifold and taper the head out to the manifold size; starting abour 1/2" back in the port..This give you a venturi affect and the velocity of the fuel going in loads the cylinder for excellant torque. That's what you are really looking for. You can put in larger valves if you wish but for me on the street to 4000 rpm small makes torque. I have never had any problem with ever taking .125" off the bottom of a head but I would not reccommend over .100" on a street engine..Good Luck..#35
