it cost like $60 for head gaskets and $40 for head bolts?
im hoping your removing the lower intake as well. if your just porting the lower and not the heads, i'd just gasket match the top and port about 1-2inches down and let it taper to stock. You'll get more velocity that way and more air.
Anyone thats just porting with low grit sanding rolls is wasting a lot of time. about a couple hours EASY. a deburr and high speed dremel works best. But the burr cuts fast, so many will see if they're using an air compressor and trying to port on their own intakes that they will port beyond gasket and ruin it
I strickly use sanding rolls when i port all my heads and intakes for my car or customers for only polishing and fine smoothing the gasket matched portion. a burr takes away MUCH more aluminum then a sand roll and will actually give you the extra volume you're looking for