Hi all,
Here is my humble contribution to this thread... maybe it helps to believe Suitbert´s theory...
It is a Ranchero case marked 2990 1 SC which sounds odd as 2990 was a sub second version,
but below there is the number 2996 without any "SC" though - maybe a "mis-cast" - 1 SC should stand in the lower line...

It is no doubt an original Ranchero case.
What me made suspicious was the dial - made in the style of Ranchero and Railmaster dials, black with the silvered numbers and minute markers,
but marked "Seamaster". The dial is a bit aged and 100% original, shows even patina and speckling" where the black paint is worn and the lower
silver "appears"... I believe this watch to be original except the sweep second hand which does not match IMO (do not know about the crown tough,
I am no expert on these references). Maybe somebody with more experience on these models can shed some light on this...
I must apologize for the bad pictures - they were done under bad artificial lighting as a quick shot to be able to contribute to this thread in time.
Otherwise I would have had to wait until tomorrow morning and my response was too late then.

kind regards
Erich