May I ask why you feel you need to rebuild the carbs? Is there a problem with the bike?
The 2003 was equipped with a 17 tooth drive sprocket. Switching to a 16 tooth will improve acceleration a bit without changing anything other than top end. You could also remove the 3 baffles in the air box which will allow a bit more air into the engine but to really gain some extra omph, the pipes should be changed or gutted (There used to be a guy that purchased stock pipes and gutted them then sold them for a lot less than new pipes or TORS). If you increase air flow, re-jet the mains at least, add a shim to the needles and remove the caps from the idle mixture jets and richen them.
https://www.triumphtwinpower.com/ has a slew of options for the America to liven things up a bit. Air box bell mouth, ECM, jets etc etc.
