with stock heads, GT40, GT40P, Windsor Jr heads, the stock Cobra lower does not really need porting. I could balance the flow of the two front trunners to the rest of the runners, and that is what I did to my Explorer, but I'm not sure that would be worth the $100 I charge. We'll see how much power my stock cammed, GT40P headed, Expolorer intaked car makes this spring.
As far as which GT40/Cobra/Explorer to use? - they should all be the same except for sensor/EGR coolant holes that may or may not be there.
scorp69 - PM me a price shipped. I'll be out of town for 2 days.