2 BBl Dual Exhaust

As has been already stated, the "Official" answer is no, if the letter of the federal law is being followed. Just like it is a Federal Offense to replace your engine with an engine that is earlier than the year of manufacture of your car. And any replacement engine must retain all emission control equipment for the year of manufacture of that replacement engine regardless of the year of vehicle. The Federal Regulations are a Toolbox for the states and local municipalities to use to meet Federal Clean Air Standards. The enforcement of any such reg your state choses to adopt is up to the state not the Feds. In any event, no exhaust shop is likely to remove a cat and not put one back "for hire" on a street driven car.

So, how do you work around this? I have a few suggestions. First, there was a 360 cid engine option in 75 that DID have dual cats and dual exhaust. So you could use factory style replacement 360 exhaust parts, with more modern "universal replacement" cats which flow far better than the original. (as original parts are possibly obsolete and out of production, you may be more free to have "suitable replacements" fabricated locally). You could also replace the original cat with a more modern "universal replacement" cat and a free flow muffler. If you plan to keep the 2 bbl, this would probably be adequate, so long as the original exhaust system is in decent shape and the original cat has 100,000 miles on it. You could and should contact the California Air Resources Board and find the location of the nearest "Referee Station". This is a place where you can get a mod certified or exempted by the CARB. By putting dual new cats on a dual system, you maintain the original functionality of the system, and in fact probably improve it's function. You will have to convince the rep and he will issue you an EO number to keep with the car (this is the CORRECT way to do it in California, other states will differ). You could drive to Reno or Vegas and look for a "don't ask/don't tell" exhaust shop. If you show up with a cat installed, the shop will be compelled to put one back, but some places will hand you a sawzall and turn a blind eye while the cat "magically disappears." You could take the car to a shop on a trailer without license plates and have duals put on your "racecar".

If it were me, I'd do a little research with the CARB and see if you can find an "approved" solution. They may tell you that being exempt due to age, they don't care. If not, you may have to get more "creative". If you end up doing something that isn't quite legal, keep the original exhaust system so you can dodge any fix-it ticket you may get down the road. Personally, I wouldn't sweat it too much. Put on some fairly quiet mufflers, don't drive like an idiot any you should be fine.