I like your hide-a-bench!
I have a large cast iron plate, that came with a plywood top. The man I purchased the plate from was 78 years old. He told me th CI Surface Plate was his dads. There are no makers markings, but it is a great old plate.
I have cleaned it with mineral spirits, and to remove canode 2244, windex. When not in use, I apply some way oil with a rag and put the top on.
Good score!
toolman_ar