If it's the regular Swiss Cheese Custom then it's the 490R/498T combo.
There are other Custom models which have Burstbuckers...
Call Gibson Customer Service with the Serial Number and they can confirm exactly what you are looking at.
I'm horrible at describing tones... but to me the Burstbuckers have a more classic rock sound where
the 498T/490R PUPs come across darker to me... Not better or worse but different.
Some excellent discussions out there on the 498T/490R and Burstbuckers...
I'd hit up the forums for some additional info.