The PI intake swapped onto NPI heads is one of the easiest HP gains you can get with the NPI motor. Even though there is a port mismatch it makes good power and above 4000RPM will give another 15-18HP at the rear tires.
Here is what needs to be done, we are using the NPI Swap Kit for the needed parts.
These instructions are only an addition to the regular instructions for changing the intake manifold. Since the Mustang, Thunderbird/Cougar, and Crown Vic/Grand Marquis/Town Car all have slight differences in the upper elbow/EGR/throttle cable setups, you need the particular instructions for your vehicle and use these as a supplement for the changes needed to fit this intake manifold.
First step is to remove the original NPI intake, heater hose beneath the intake, and the water pump.
Behind the water pump and in the valley of the engine is a water tube that must be removed. To do so take a large hammer and hit it towards the front of the engine like in the picture below:
Now install the new PI water pump nipple from the front of the engine.
Next step is to install the new all steel PI heater tube and it will fit like the picture below:
And here is the view from the rear of the engine showing where it bolts to on the drivers cylinder head:
Next step is to take the intake gaskets and remove these clips/pins. They are designed to locate the gasket on PI heads but need to be removed for NPI heads. The intake bolts will locate the intake gaskets well enough.
Here is the location that you will need to place a dab of RTV to seal the water jacket of the head to the intake gasket since they are slightly different shapes. I know you see that port mismatch but do not try to gasket match the NPI head as it will not flow anymore doing this.
And here is the blob of RTV you need to place at the corner only. Make sure you clean the head really well before doing this. There have been literally hundreds of these swaps done and I have never heard of a leak being reported here. You will need to do this at 2 locations, the passenger front and the driver rear.
With the RTV still wet install the intake manifold and gaskets and torque to factory specs. Allow the RTV to dry for a few hours before adding coolant back to the system.