Well the basic gasket matching, short radius, valve guide, and polishing the exhaust port/combustion chamber work are pretty much the same. The main thing is the vertical emissions shroud on the intake vavle that needs to be laid back and blended into the chamber. If you are going to be doing all this work you should consider having PI intake valves put in and a good seat job done. The main point of porting the NPI head is to increase it's low lift number because it already outflows the PI head at the higher lift (.500 and above). Not too sure about any site with a "How to". . .
I'm about to port a set of PI heads that I bought. Sure I'm a bit "nervous" about puttig them under the knife, but I know i will enjoy the benefits. I am going to start with the lightest abrasive I can that will take off material and give me the surface I want and just take my time. I'm not doing much other than the basics really. I got my info from the June 2004 5.0 Mustang and amazingly I retained it, lol. I wish I had it to look at, my roomate flooded the bathroom floor and ruined my two latest Mustang mags....