I had some "porting" satisfaction (but not on the heads) when installing an Eldelbrock Performer 289 intake on the Explorer engine I swapped into my Mustang. I did not port the heads at all, rather I ported the intake to match the intake gasket where the gasket was bigger, and trimmed any gasket edges that may have been obscuring the exit of the intake. For the most part the intake port on the head was larger - so no problem with the flow in as long as it is running downhill past the drop off.
Same theory on the exhaust - trimmed the exhaust gasket where it obscured the exhaust port, (the ports are kid of ovoid) then ported the entry of the cast iron replica 289 HiPo exhaust manifolds. It is a street cruiser so I want off idle response and it never sees over 4-5K rpm typically. It has a stock Mustang 5.0 Cam and I'm not sure it is any different than the stock Explorer cam. Running through stock Mustang dual exhaust with the tranverse muffler. It's a somewhat worn out old engine. With a 450CFM QuickFuel Carb it made 205HP/270TQ to the rear wheels through a C4 automatic.
Hope that helps!