I would agree that the crown is likely a replacement as it appears smaller than what would have been on a 3647 in that range. Sourcing the correct unsigned crown will likely be difficult and will take some luck, that's for sure! Good luck with your search! In any event, a very nice 3647.
: And a side picture. It was suggested before that the crown might
: not be original, but does this confirm that to be correct ? How
: would one go about sourcing the correct crown ? Then the tension
: ring is missing and I need to get that, but also the dial shows
: some staining. Is this something I should try to get cleaned, or
: is it best/safest just to leave it as it is ?