-Intake=yes
-Intense PCM=yes
-Flowmaster Hushpower Muffler= no hp gain, all preference
-High Flow cat and U bend delete=go headers
-resonator delete=might cause car to sound raspy
-180* tstat=yes
-3.5 or 3.4 pulley=with all the mods above, you should be good for this

as for headers buy these!
PONTIAC GRAND PRIX GTP 1997-2003 STAINLESS HEADER 3.8L : eBay Motors (item 180490883199 end time Jul-05-10 18:24:15 PDT)

same design as the SLP knockoffs that is SSAC