The manfacturer was the Burt Co in MA.
HH says the rectangle mold was distributed by Western Club supply.
I was privy to a couple of Burt records that showed Langworthy distributed the mold to The Royal Nevada, LV in 1955. From what I was told it was more or less an open mold in certain years.

Langworthy is no longer in business. Langworthy also distributed rectangles to the Dunes. I believe the Langworthy records exist. I was told to forget it when I ask to see them.

The Burt records exist but are only good for Inlay chips not hot stamps. You can forget about seeing them also, at this time.