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The only blocks of metal like that I've seen were for a copy lathe... but I have no idea, sent the link to some friends to see if anybody ever seen the like!

Ahh, sorry, I read it like that when you wrote non-ferrous!

Ferrous works fine too, like this one; Polierstahl (Uraoshi) | DICTUM GmbH - Mehr als Werkzeug
My father have some old Swedish cast iron plates that has been flattened and used with SiC for plane...

Well, you can hone on brass, I've cut and fasetted precious stones on brass, copper, aluminium and tin, all you need as something on them like diamond, SiC, tinoxid or the like, you add it as paste...

"His wife said they were used to cool the blades after sharpening. "
Say what?