Craig:
I think the 58mm answers the question. Thanks to the grand efforts of Hans Pfingsten & John Mann compiled in DGJ Winter 2005 at page 177 notes that typical German doubles from the period measured 48mm while the Daly/Lindner/Sauer boxlock variants were 56mm and their sidelock cousins measured 62mm.

Kind Regards,

Raimey
rse