for sure his family/roots came from czech heritage (as manny families would come from to vienna during the austria-hungarian monarchy the turn of 1900 due to unemployment......) and DREVO (in czech =wood) would be most likely pronounced in vienneses dialect like DREWO, which (like in manny other cases) would change the spelling of a slavic name over the time......but from memory his name he used as artist was DREWO....