ShopTalk is your friend......
http://www.valkyrieriders.com/shoptalk/truckstackinstall.htmTo answer your first question, no, you do not have to remove the rear baffle section to install truck stacks.
The basic idea behind cutting off the rear of the exhaust can, ie, rear baffle section, is so that one can have a louder exhaust.
As in Rio's idea, you can reinstall the baffle section when one wants a quieter exhaust.
It's the same idea behind MarkT's silencers. Take 'em out when you want loud, put 'em back in when you don't.
Alot of folks gut or take out the rear baffle section only to find out that the newly induced drone drives 'em nuts.
That's the idea behind putting the baffles back in.