Well done, Woodinsight!
It's a 1929 Rumpler design indeed, with his Rumpler "Vornantrieb" system ("Frontantrieb" was already patented by DKW
)
However, during the course of this puzzle I've been digging deeper into the history of these trucks and I'm not certain if it is the Luchterhand & Freytag truck in development.
This is wat I found: Since Rumpler now had no own workshop, he founded the "Vornantrieb- und Vertriebs GmhH Berlin-Charlottenhurg" and contracted other companies for building cars. On the 21st of October 1929 at the Prague Motor Show in Vomag presented a bus chassis with "Rumpler Vornantrieb". The rear swing axle construction allowed the use of a central tube frame.
But Rumpler encountered patent trouble with Tatra over the swing axle design. Rumpler also devoted himself trucks, the best-known was a three-axle truck of the Ullstein publishing house. The body came from Luchterhand & Freytag, a 150 hp twelve-cylinder Maybach provided ample power.
So, after all it still might be a Vomag omnibus chassis!