A photo of the broken part might help. I searched my 1937 Hollander automotive parts Interchange book and it lists 1922-28 Big six but gives no interchange for the complete rear axle assembly. Under the interchange for differential, model 33,35, Big Six-35 & Royal 8-37, and early 37A are listed together along with various trucks and DuPont. A note says there is no data available for the case. This must be a pretty heavy duty differential. Search the internet for the Chandler Cleveland Motor Club. Someone will help. Maybe someone can bring one to Hershey and arrange to get it shipped in a container along with parts purchased by other European hobbyists.