If you've got an RS192 then you won't be able to do it. The centre res appears to go internally from 2" at the inlet to 2.25" (?) at the outlet- so you'd need to replace that.
PS: The stock cat inlet is 2.5" and the outlet is only 2" outside diameter!
PS: The stock cat inlet is 2.5" and the outlet is only 2" outside diameter!