There were many custom body companies here in Europe that made special bodied cabriolets (and other body styles as well).
Here is one for example made by Langental in Switzerland:
Here is a photo of a special bodied Cabriolet made in the Czech Republic:
Here is an original inside photo of the Habsburg Cabriolet that was originally posted. Note the trafficators and the position of the trafficator switch in the center of the dash rail. Also note the fold down vertical window frame chrome piece at the rear of the front passenger window :
...and an era photo of Frau Lo Heymann enjoying her new Gläser (?):