84LX89GT is right. You don't want to polish the lower intake, or the intake ports in the heads. You don't want to go any further than 120 grit cartridge rolls with it.
With stock untouched heads I really don't think there is a lot to be gained by porting the intake, but I'm sure it wouldn't hurt. You'd gain the most horsepower if you pulled the heads and did some work on the exhaust side and in the bowls. Then a gasket match on the intake side would be more beneficial. I saw an article where they picked up 30hp just by smoothing the short-turn radius, which is the area under the valve head that makes an abrupt turn into the port.
If it were me and I was going to go to all the trouble to pull the lower intake I think I would go ahead and pull the heads and rip some metal out. There's a lot to be gained on a set of stock heads 
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Project: 1988 Coupe - EFI 5.8L Twin Turbo with Victor intake, Canfield heads, F303 cam, March aluminum underdrive pulleys, TKO (or T56 if funds permit), PBR twin piston calipers and 13" rotors up front, 94 Cobra rear calipers and 12" rotors on the rear, 3.73's, Griggs K-member, tubular front control arms, torque arm and panhard bar, polished 99 Cobra wheels.
"The GR-40 kit installation is now complete, and the humble Fox-chassis car will now out-corner and out-stop a ZR-1 or a Viper, and support massive horsepower additions with perfect balance."
Griggs Racing
ICQ# 42269241
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