16MS Matching Crankcases

[59G3LS]

I have a basket case 56 16MS and the crankcases don't really look to bear the same external markings/stains etc. However the rest of the bike is authenticated matching numbers from Feb 1956, so no real reason to doubt it.

The crankcases have internal stamped markings: Drive side has "4 BN 56" with possibly an unreadable number after the 4. The timing side has "48 BN 55".

Very cryptic, obviously the drive side is 1956 as per the external markings. That would agree with the 56 stamp internally. The timing side, having a 55 internal stamp would maybe suggest that it should have the lower cylinder oil feed but it doesn't have that, it seems to be 56 or later.

Could it be that the internal stamps are sequential? Coincidentally numbers 56 & 55? Could BN be a machine operator?

Hopefully someone on here can cast some light on this?

Regards - Mark, Perth Australia