ok, this is getting out of hand. for 400 bucks you are limited. some of the mods mentioned you wont be able to do on 400 bucks unless you get killer deals on ebay or something. any pipe you get will be better than stock. better flow, lighter, etc. toomeys and shearers are good pipes, problem is they are loud. any aftermarket pipe is gonna be louder than stock. and 96db is not that loud. sometimes if you keep the silencer packing good, it will stay quiet.
i say for 400 bucks, start with exhaust (find a used pipe you like.) reeds (dual stage boyesens). thats a good start. see how much cash you have left. 14 tooth front sprocket is another good mod. advanced timing is another
most likley you wont find a +3 stroker crank, or get porting and other mods for 400 bucks. start small and work your way up. bolt ons are great and cheap ways to make power. but make sure your parts will work together.
btw, a sparky doesnt really quiet the exhauist much, dont believe that. all it is, is a can with a screen inside to keep any flames from exiting. it arrests sparks, not sound. it may have some packing, but i doubt it. if it does muffle any sound, its not much.
do some research beofer buying pipes. thats where a lot of power will come from in your case