There were actually a few LS6 Novas built by Jim Wangers Chevrolet (the same Jim Wangers of Pontiac fame) in 1973. Wangers bought a couple dozen LS6 crate engines and offered them as a conversion in the Chevelle, Nova, and Camaro. In Wanger's book "Glory Days", he describes how he got into a lot of trouble with the EPA.
Jim Wangers complied with the EPA laws. He had buyers of LS6 conversion cars sign an affidavit stating that the vehicle would be used off-road only. In order to circumvent the strict EPA policy that a dealer could not tamper with ANY emissions devices on a new car, Wangers would have a buyer buy their car, drive it around the block, then bring it into the Service Dept. That allowed him to get around the strict EPA policy of tampering with new vehicle emissions equipment, because technically, the car was no longer "new".
Then one day a young couple bought a new 1973 Nova 350, and had Wangers Chevrolet drop in an LS6. Under the terms of the agreement, the owners had to trailer the car off the lot, (which they did), and they signed the affidavit that it would be used for off-road use only. Wangers also took pictures of every LS6 conversion car he sold, sitting on the owners trailer, just to make sure.
But a few months later, the couple got divorced, and the wife got the Nova in the settlement. When she went to get it registered, it failed state inspection. She talked to a lawyer, and the lawyer demanded that Wangers Chevrolet buy back the LS6 Nova, or replace the LS6 engine with the original 350, then reinstall all the emission equipment. Wangers refused, citing he had the signed affidavit and an agreement that the car was to be used off-road only.
The lawyer contacted the EPA. The EPA was not amused, and after investigating, they fined Wangers $500,000 (around $4 million in today's dollars), which was an outrageous amount of money for a dealership to pay. Wangers decided to fight it.
The EPA was already upset with stories coming in from all around the country about dealerships removing emission equipment, from AMC to Chevy, Mopar to Ford. Many high-perf fans still wanted that pre-1971, high octane horsepower, and disliked EGR valves, charcoal canisters, and 87 octane unleaded. So the EPA decided to make an example out of Wangers Chevrolet. Wangers name was well-known in automotive circles, he was the father of the iconic GTO, and hard-core auto enthusiasts knew about Royal Pontiac from the 1960's days.
Wangers could not afford to pay $500,000, so he agreed to be a scapegoat for the EPA. For a much softer fine of $500.00, he agreed to reinstall the woman's 350 engine, and stop performing engine transplants. The EPA blasted the story across every media outlet they could find in order to discourage other dealerships from tampering with emissions.