Not quite. It was the GKF125CE which, as I’m looking now, it looks similar to the Bosch Blue GMR 1 but not quite the same.
https://forum.v1e.com/t/help-with-new-tool-mount-for-bosh-trim-router/32861
My plan was to have a generic “blank” from which I could just subtract the tool shape (even an irregular tool) and presto I would have a mount for an arbitrary tool, provided I had a good enough 3D model of the tool.
Given this subtract-the-tool approach, it’s simple to make a mount for a 50mm cylinder. Although now that I say that out loud, I need to check if it will actually clamp the cylinder or if it will simply fit but not grasp it.