According to a book I picked up last week.... Coupes were not allowed to run in SCTA sanctioned events until 1950, when SCTA established a Coupe class. Pg150 The Birth of Hot Rodding The Story of the Dry Lakes Era by Robert Genat
According to Robert Genat and Don Fox in their book "The Birth of Hot Rodding," SCTA established a Coupe class in 1950. It is on page 150, in the photo caption under the Pierson brothers' coupe. Edit: I guess I need to learn to type faster......
Edit: After a bit more looking the Rusetta Timing Association allowed them with it's formation in 1948.
I believe that coupes have always been able to run at Bonneville. The classes at the first Bonneville meet in 1949 were, as far as I can tell, Roadster, Lakester, Streamliner and Competition Coupe. Sedans and Motorcycles were not allowed to run until later. Remember, Kenz & Leslie ran their twin engine pickup at the '49 meet. Mick