Muscle Car Review (May 2000) did a spread on a '73 BM Chevelle, 427 L88 Phase III. Owned by Tom Cahill at the time of publication.
The article stated that it was the only one built, and that it was the last car that Joel Rosen built before the EPA came to visit him. The price was $12K out the door, which was equal to the gov't average for one years wages for '73.
Silver car with custom side pipes and swivel drivers seat.
I will try to scan some of the pictures, and post them if they look OK.
Andy