The company Seld-Kompressorenbau-GmbH, from Heidelberg, made an engine with two opposed cylinders named “Seld F-2” giving 36 CV. This was in the year 1938.

From Appendix 12: (Seld Kompressorau) Manufacturer of compressors and small aviation engines for motor sailboats, etc. Years before WWII.

“Seld engine of 20 HP at 2800 rpm”

-We have also recovered a photo of a 36 CV with the same architecture.

“36 CV Seld engine”