In colorado springs I ran into the same problem. On my mustang it came stock with a single exhaust and because of that it needed to only have 1 cat, in order to dual it I would need to do it after the cat
that makes no point of dualing the exhaust but they wouldnt let me run 2 cats. Of course I also got introuble for converting to EFI from the stock carb system. When tested I had way less polutants then I was allowed but got failed beause it was a different set up!!