Here is an attempt by my friend Robert Bank to demonstrate to some extent what the stencil for the cover of My Own Mag #5 (The Tangier Issue) would have looked like.
And then there is Jeff Nuttall's published cover (in green). Nuttall's work with the stencil is really amazing when you consider the mix of visual and textual affects he was able to generate.
They are so good it makes me wonder how much of My Own Mag was actually done with stylus and paper stencils with a mimeograph. Nuttall did several covers for Bob Cobbing's Writer's Forum and many of those covers were drawn by Nuttall and printed using offset lithography, while the rest of the publication was off the mimeograph machine.
If anybody can take a look at the complete My Own Mag (http://realitystudio.org/bibliographic-bunker/my-own-mag/) and determine how it was created please contact me at email@example.com.