Congratulations to dracu777
I put in hours on this puzzle and came up with absolutely nothing but looking at maybe 200 photos of the 1935 540K convertible coupe by Erdmann & Rossi that is an almost exact duplicate of this 4 door cabriolet.
I never even thought of Englehard but once dracu777 mentioned the name I did further research. One usually reliable source indicates it is on the 230 chassis and dates from 1937. I will do some further research, but in the meantime, does anyone know for whom this puzzle car was built. The convertible coupe was commissioned by Daimler Benz for the King of Iraq.
Bill