I think you'd want to see the dial in person to see how metallic it is, but the photos do show the vertical brushing characteristic of a transitional dial. I'm a bit further away from Prannerstrasse to check than you are!

Does the serial fit well within the timing of the transitionals? Somewhere around the mid- to high-157s?

The movement won't be the original though, a Cal 12 is too late to be in a transitional Monaco - we're already into regular production for some time before the C12 appears.

So original watch with the movement replaced somewhere along the line would be my impression from what I can see - as it's "aus Erstbesitz", the original owner may recall having sent it to Heuer for movement servicing and the resultant change.