Are you referring to the SuperTrapp SE series (the old Harley performance mufflers) which have the interchange able end caps? If so I think the baffle is different and does not have the disks which effect sound and power.
The standard baffles for the SE are a cartridge type baffle, there's nothing to repack, and they aren't straight through. I believe that you can get a Kerker baffle from Supertrapp that fits the muffler bidy that is straight through, and louder.
They were the old 65115-98b mufflers, and I gather that the Moco is making them again for the '10 model year bikes with the cat in the headpipe.