bypass cat and muffler???

Check your states laws about having your vehicle inspected. Most states have come to realize that since older cars make up such a small percentage of vehicle miles per year it's pointless to test them. California I believe is one.

Now as for your cat. Is it the original? If so it probably quit working long ago, and should be replaced. Is it the old school flat "stop sign" looking unit (pellet type)? If so it is highly restrictive and should be replaced. Modern honeycomb cats cause virtually no restriction, and aren't terribly expensive.

You could also run without it. Your engine would likely run cooler, and get a little better mileage. Not sure I'd run without a muffler. A stock unmuffled slant won't sound more powerful, it'll just sound like it needs a muffler.

Anybody who says you "need" backpressure doesn't know their a$$ from a hole in the ground, much less anything about cars. Backpressure is, and always will be the enemy.