Hows this for an important drawing, as we are discussing diffs.
1981 I was studying design at school and the project I was working on was to design and build my own r/c car. I contacted Schumacher for help with designing the diff, and Cecil sent me a photocopy of his drawing of the first diff he designed for Robins Mardave car. You can see two options with different wheel designs, one being a new wheel and the other being a modified Mardave wheel. You can also see the first design also included a wheel cover.
To see it clearly I had traced over it, and this has helped preserve the drawing. Unfortunately a change of schools meant I never completed the project, but thankfully I kept my notes including this drawing.