Depending on computer engine management you may have two o2 sensors or just one on each side. The setup with 2 has one before an after the cat.
With the one before and none after the motor will run fine without it.
It is illegal to remove emission equipment.
At the sometime:
CAFÉ Standards. The U.S. Congress first established fuel economy standards for new passenger vehicles in 1975 as part of the Energy Policy and Conservation Act of 1975. These standards are known as the corporate average fuel economy standards (CAFÉ). The CAFÉ standards are the sales-weighted average fuel economy, expressed in miles per gallon, of a manufacturer's fleet of passenger cars and light duty trucks (vans, minivans, sport utility vehicles, and trucks) with gross vehicle weight ratings (GVWR) of 8,500 pounds or less, manufactured in the United States, for any given model year.
Vehicles that have GVWRs above 8,500 are not subject to the CAFÉ standards, so certain heavy vans, sport utility vehicles, and pickup trucks are not required to be tested for fuel economy or included in the CAFÉ standards. They are considered heavy-duty vehicles under federal law. Passenger car standards began with the 1978 model year. Light truck standards started in the 1979 model year for vehicles up to 6,000 pounds GVWR and in the 1980 model year for light trucks through 8,500 pounds GVWR.
Check to see if your state had more stringent standards or inspections.
Some do some don't.