Supertrapp 4" race series FTMFW!! LOL, na, whatever floats your boat man, I'm just boasting the Trapp cause I have one, haha! The pipes that '98 listed are supposed to be Good, LRD is also pretty proud of theirs, maybe it's worth a shot, idk.
Most guys say for all around good power a Web .390 & matching springs. You could use the Wiseco piston 1mm over for a semi big bore. At 1mm it'll yield a lil more compression than the advertised 10.25:1. A carb upgrade & a custom FSR Airbox by Weston! Na, those are one off & I'll have the only one in existence! Choices are pretty limited for airboxes, most guys just upgrade the filter & cut the top out of the lid. CFM Makes one but I haven't heard much praise on it. Good luck!