Model of my watch

Hi all, I have had this watch since 2012. I wear it sparingly as it needs its second service (the first in 2015 left it with some issues unfortunately). A few years back I ordered one of those Archive Extracts from Omega. On the paper it lists the watch as ST 131.004 (Watch Ref) and states under metal that it is stainless steel. In looking up the ST 131.004 I keep seeing gold plated watches. Was there a full steel version also offered, which mine must be? My first thought was my watch may have been stripped of its original gold plating at some point, but that seems unlikely as the dial shows no signs of plated markers. Thoughts? Here is a photo of my watch. Thanks in advance all.

Thanks for the reply, and info. Much appreciated. I was a tad confused as I have seen a few plated cal 600 watches (look just like mine, but plated with gold colored hands and markers on the dial., where the caseback says 131.004 as well.

I actually did find one several minutes ago. It was posted here in 2015.

Here is a more or less identical example to my watch that was posted here in 2015.

1964 Omega | Omega Forums

Interesting to know. I was a tad worried I might have a franken. I do know the crown is not correct for this model. How difficult would it be to source a period correct crown?