All,
Thanks for the info everyone...While I was under the impression they were slate, I was gonna make the wife an island for her kitchen. Once I discovered they were polymer, something super durable for reloading came into view. They have the holes punched for the usual gas burners (3 across) close to the edge.
WV_Visla & All4eyes: Thanks for the info about asbestos. I've seen mention of bakelite use in the 50's which is about when these would have gone into service...but you never know. I'll use a respirator, eye protection, & gloves to play it safe. Grind while wind blows the other way.
Bullseye308: I'll shoot you a pic tomorrow and you can let me know if you're interested in one of the spares. They are super-heavy and hard as nails.
bcurry