hit any small track in your area, most of them still run a "stock" class.
some stuff has to be done for safety like adding roll cages and fuel cells and removing glass, and you can do some lighter mods on your engine, but they mostly don't do alot.
here in MI we have two classes of street stocks; regular, and 4cyl engines.
NASCAR is restricting new owners to 3 teams. Existing multi team owners are grandfathered but when they're gone they're gone.