The Corvettes and Porsches came around in the mid 70s--after the heyday of the series. Those cars were not really 2-door "sedans" or ponycars, and they sidestepped the original SCCA rules a lot. A Corvette or a 911 were never and will never be in the same class of cars as the Mustang, Camaro and Barracuda.
The legal bodies are the ones listed on the USVTA site, and until HPI, Protoform or someone else comes up with one of the ponycars from the era the rest of the bodies are from, the list is what it is...