Regarding the tail, you guess correctly, but it's not an Argus!
Aircooled inline engine, not German, it switched manufacturer at about the same time as this aircraft was built.
Edit: Clue time!
The engine was not built in the same country as the airframe and the airframe's designers took as a starting point someone else's existing and agile sailplane that itself went on to established a world speed record.
Last edited by SincoTC; 2nd Nov 2011 at 21:23.
Reason: Additional clues