Hi Dale,
You may not know but the BRCA is very strict on what bodyshell they deem legal, although in recent times they haven't been as much as they used to be.
Anyway here's a copy of the rule book:
Must be representative of a ‘full size’ Touring Car or GT (Racing version or Road going) i.e. NO ‘designer’ type shells.
No NASCAR, Rally, Truck or ‘Pure Racing’ type
bodyshells allowed.
When they say representative, it means that it must look like the actual car to a certain degree, which is purely subjective and obviously depends on the person who checks the bodyshell.