You probably mean the Mechboard64. There’s been a small group buy years ago, and I think the project has been open sourced since, so you can get the files for the metal bracket (plate) and PCB and make them yourself.
Like you say, it’s meant to be used with the OG keys by using 3D printed adapters.
It cannot be used with modern keysets because the 1.5u keys on the C64 have off-center stems, so the plate / PCB layout is wrong.