Many people make a business of taking stock cars from the assembly line and customizing them. But one which is factory-modified would be a special edition or one-of-a-kind vehicle built by the original manufacturer, in this case, Honda. I don't know if the Civic GX is what they're referring to. I have a Civic Si which has a racing package. You could say it's modified from the standard Civic. But I believe it's still considered a stock car. I think the same is true of the GX. I think they make a lot of them.
I believe your excerpt refers to a GX which has been
further modified at the factory to run on LNG. They may have produced only one of these factory-modified versions, or they may have produced a thousand.
- A.