Just got the parcel, it is probably equal to a BTMC version from before 1930, but I am not able to identify it so far.
It came with an odd Siemens W28-ish handset (not pictured here) The dial spring and spring-holder is "repaired" so it does not work, hopefully I may fix it. The hook-switch is missing the insulation part that shall activate the springs, still interesting.
Pretty close to BTMC 396A but still not equal.