I'm glad I'm not the only to have tinkered with the stock ones. I have completely removed the back baffles on both my Americas and I'm completely happy with the sound they make. And as you say it's free!
And I haven't needed to rejet, or play with anything else and they both run fine...just ask anyone who trys to keep up with me!
Gina
03 America - Pretty stock - except the TBS wheel...

06 America - missing, presumed in bits. With it's TBS wheel...

09 America - It's very blue....