With race cars, I think the chassis rather than the body defines if it’s “real”. I know one of the original Posey Challengers was restored from a chassis. It was raced through the 70s with other bodies after 1970, GM bodies if I recall correctly, in different classes of racing. The chassis was later ID’d as an original Posey chassis and restored back to its original 1970 Trans Am season glory.
Vintage race cars are a different animal than stock vintage cars. Engines were changed routinely and bodies were repaired and replaced after accidents or to repurposed for another season or different class of racing. Numbers matching and original sheet metal rarely exist in that world.