I just noticed the 6.3's you are looking at are Parallax...ick...errrr, his felt is SOOOOOOOOOOOOO thick, adding anything I think could introduce instability honestly.
You could ask him to mill them to size, and to use thinner felt than he usually uses.
Or Peter Tan.
What's wrong with the Intes cradle anyway? If you need to mount something else, there are other ways than using seperate rings etc. Think outside the box
