Not the only one, but one of many; a Porsche 928 Convertible (Cabrio) was introduced by Buchmann in 1981.
This green 928 is the first Buchmann Porsche 928 Convertible, presented in 1981. It's clearly different from later B+B Porsche 928 Convertibles with details like the small B-pilar that was discarded in later versions.
Probably on of the early production cars, this white Porsche 928 Convertible by Buchmann.
Text: copyright Bram Corts