I think these are way cool, and great looking, and I have never seen, and can't find, another set like them. They're made of rubber, which is pretty firm but a little squishy too, with embossed letters and numbers on all sides. I love the bleed on the green especially, and the crusty surface of the rubber all over--and they sit in a great old  box/holder made of wood from old crates, joined with fat nails and I'm sure made for them long ago. Definitely these are pretty early, late 19th century or possibly very early 20th.

They are fairly large--1 1/2" cubed. The holder measures 8 7/8" x 8 7/8" x 2 1/2". The blocks show wear and plenty of age but are in good shape. There is one blocks that shows some loss, pictured in details--4 photos of the same black from all sides.