You aren't wrong, those are the exact pieces that come with those cans. They also have little effect on the exhaust flow when they are installed....I know I HAD them too and saw what they did on a dyno.
If anyone needs them, I have a set of the SBK db killers (in titanium) that I'll sell. Beautiful pieces!
Bit of archaeology here digging up an old thread but I have the same issue as the thread starter and there are at least two different db killers called "31" to the Leovince SBK, one is 50mm diameter and the other one is, hopefully, 48. They have the same model number of course to make things easier.