I'm so pleased that it's been solved. I was having sleepless nights.
I've found the race results for that event, but I didn't manage to find any internet reference to this car or any image. I think the FIA changeover for enveloping bodywork was 1953, so it's interesting that the German authorities decided to change the year before. I should have realised that nearly all German race circuits had cobblestones at some place or other!