Blower?

[Hammer]

Most shops who do the swap sell swap "kits" that include all that is needed to perform the intake\heads swap.
There is usually a gain of around 50-60 hp at the crank after the swap on an otherwise stock setup...

Tireburner is correct about the increased compression ratio when using the PI head swap....

Another option is more expensive, but blower friendly....
The Ford motorsport Intake and Heads.... expensive yes, but if you take a look at my numbers with a low boost setting and a conservative tune you'll see that you can take that setup quite far.... especially if you went all out.... (Blower cams, forged internals, 10 psi pulley, aggressive tune...)

All I know is that you don't want to put boost on that stock intake.... it WILL go bye bye. Mine did after about 2 weeks on the blower.... and it IS NOT covered on a TSB like the 96-97 intake.

A good mid-cost solution may be a roots type blower....
Replace that crappy intake with a blower!
I think Ford Motorsport, Saleen, and Kenne Belle all make kits for the 98 GT....