Okay, so these are not the 'money shot' photos. But very interesting. As [MENTION=19743]USAZorro[/MENTION] pointed out, the under-the-bb cable routing is strange. The reason it's strange is that there is a single cable stop at the bottom of the down tube; and the derailleur is a post-1967 Record without a cable stop. This frame was made for a derailleur with a cable stop. I'm not sure exactly what that means, beyond the fact that this frame was not made with this derailleur in mind.

And what about the 531 decal?

When did they start using decals with TI REYNOLDS LIMITED verbiage?

I'm inclined to think this frame is from the early 70's, or possibly the late 60's