Get one, but do 3.73 gears (if it's manual, 4.10's if it's auto) FIRST.

Then, piece together a supercharger kit. Mustangforums had a write-up on piecing one together, find a cheap head unit and then just buy the accessories from the company. Mustangs stock come with 2.73s and optional 3.08s, so the gears help a lot. Also, get a pro 5.0 shifter. If you want it to handle better, a set of shocks and springs will help; just cutting my springs helped... they tend to sit pretty high, giving a high center of gravity.