What i thought Dave was saying is that why would you worry about the legality of your cat when there a visible defects on your car as it is, and when you get sent to Regency you will need to change everything anyways. When driving these sorts of cars there is always going to be a defect, Or your car would be stock as a rock!!
I say dont worry about your mods legality, within reason, ie not putting 22s on it!!