I hope, I described as clear as possible, what I understand by the question 'German one-off of the 1940s'. It describes exactly a car, only one time built in Germany, between 1940-1949. No more, no less.
In case I confused you, I will provide further hints:
1) It is British (not German)
2) It is a one-off
3) It is of the 1940s
4) I have no proper name for the car, but the name of the builder
5) I have little information about the engine of the car
6) I have another picture of the car, which I attached to this reply proudly
7) I will UNLOCK to give everybody a next chance to solve this puzzle soon
Trust me, further helps and hints are guaranteed, to get all my remaining puzzles solved as soon as possible