What do I need to PI swap my '96 Ford Mustang 4.6L?

You just need the the P.I. heads and Intake manifold. I think there's a coolant pipe that get's switched out located in the valley of the block.  P.I. heads on a non-P.I. block with non-P.I. pistons. will raise the compression up to around 10:1 (or thereabouts) so you'll have to run premium fuel going forward. The upside is that you'll end up with a bit more power than a stock 99-04 P.I. 4.6L. 

The PI engine is virtually identical to the engine in your mustang in every way for that year. The only differences are the PCM is tuned for slightly higher idling speeds and later, firmer shifts, along with physical mechanical differences such as an oil cooler, aluminum drive shaft instead of steel and a shorter final gear ratio (usually 3.55 as opposed to a 3.08 in regular civilian crown vics). In later iterations, the cooling system capacity was increased in PI cars as well due to how much time they spend idling. 

1) Why waste your money? That's possibly the ugliest Mustang ever designed.

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2) Google has existed for 22 years. It's about time you learned to search the internet with it.. This guide took me all of 11 seconds to find:  https://www.stangnet.com/mustang-forums/threads/np...