Clay:
Thanks and I wish I could take credit for it but there are bits and pieces of info out there already compiled by someone and it's just a matter of finding it and putting it together then guess at the missing puzzle pieces.

Ernst Kerner peddled a few sidelock drillings with a similar safety in the same location.

FPH: could you post a pic of the marks on the top tube?

Kind Regards,

Raimey
rse