Cal 8531 - Any idea what year and reference?

Another image:

Looks like a ref 803

I'm starting
to learn a bit - this is the case back. So it's a 603A? Any idea what year?

The 603's are essentially (slight case amendment) early '60's versions of the
mid to later decade 803's

Nice watch

That would fit with when I think it was bought. Thank you!