Please ID the builder of this racing car and the engine source for a point
Experts?
East German (former German Democratic Republic, GDR), probably one-off
not from the Eastern part, but a one-off nonetheless
French?
no, as I mentioned from Western Germany
Professionals?
Prewar engine ?
Adler-based?
prewar-engine, not Adler based
Hanomag?
no
BMW as usual?
yes
Otto Schöpflin 1949 in his converted BMW328?
no
Well, it looks the same car to me. Perhaps just another driver?
apparently you are right, this was the Schöpflin eigenbau, but it was modified by its new owner/driver. Locked for you to find him.
In 1949 former WW2 fighter pilot Theo Weißenberger acquired the Otto Schöpflin BMW 328 Eigenbau which he further modified. At Saarbrücken he came 5th in the 2-litre class. However his career was cut short, when, having survived the war, he was killed racing his BMW-Weissenberger Eigenbau on the first lap of the Eifelrennen at Nürburgring on June 10th, 1950.
And another point to you
Otto Schöpflin 1949: