FC980C (Topre) and FC980M (Cherry MX) keyboards made by Leopold
https://youtu.be/LwwIYJxDdAU?si=WaJhQQFKCleWgRqs
The aluminum version weighs in at almost 6 pounds (3kg) with the keyboard installed.
The Veracity Steel version: around 11 pounds (5kg).
Dimensions are: 412mm x 161mm x 32mm (at tallest point).
Typing angle: 3 degrees.
All threaded holes use M3 tapping.
An adapter plate holds the breakout PCB in place against the housing, supported from below by the rear cover plate.
Replacement adapter plates can be machined with CNC or sheet metal fabrication techniques.
Ours were 6061 Aluminum, Clear Anodized (Type II), but any aluminum should be fine, and anodizing isn't necessary.