Just glancing at it, i'm guessing 1954-55.
The corroded crap around the yoke is the yoke cover plastic used in those days... popular for breaking down over time. They say WalMart bags will take millions of years to break down in landfills... but yet yoke covers of the mid-50's to early 60's fall apart after only a few decades.
Typically, if you needed a new yoke, it did not include the cover... which is what fell apart later in life.
Yours doesn't look too bad yet. As long as you don't attempt to disturb it, you will likely be okay.