Read clockwise
I started out with the sketches above. As mentioned I decided to start building a first version about halfway through this process to help me figure out the details of the design better. The hands-on 'tinkering' did help!
Since I wanted my 'block' to be an actual cube shape, my first version did not work. I only released after making two of them that there was no way of fitting them together. The solution was to use some basic math and account for the lack of width when using the shape I designed diagonally.