1680 2-Tone - Conversion or True Custom?

[GP_Pirate]

A couple of days ago I posted a question about a steel and gold 1680 that I purchased new from an AD in 1980. The AD stated that it was a special/custom order by a customer who later backed out of the sale. I have the all the orignal boxes and paperwork, including the punched warranty card. It was purchased at a Baily Banks & Biddle store that has since closed. I have emailed corp headquaters to see if they have the orignal invoice from Rolex and am awaiting response.

The consensus from members overall was that a true custom 2 tone 1680 was relatively unheard of, and that all known examples were found to be conversions.

A couple of members suggested looking at the inside of the caseback since true customs have the ser # engraved there. I have since taken their advice and have attached pics of what I found. As you can see the ser # is indeed engraved on the inside. There are some other markings I am unfamiliar with.

The watch has been serviced at a Rolex service center twice. I contacted them but they said they do not have records on the original build, although their policy is that they will only service watches that are in the same confiuration as when shipped.

Please share any thoughts you have on the authenticity of this piece.

Thanks so much for any help.

Glenn