[update: better pics on my personal blog]
Posting this here so it doesn’t get buried in the workbench thread.
While perusing Google Books I ran across an unusual leg vise arrangement on a Nicholson style bench in Farm Woodwork by Louis Michael Roehl, 1919. The leg vise has two angled braces rather than the usual pin bar. The angled braces, along with the screw, form a triangle that rides underneath the top keeping the chop parallel to the leg. As the vise attempts to rack, the downward force pushes the tail of the bracket into the benchtop keeping it level. The pictures explain better.
The book can be found free online at Google Books, archive.org, and wkfinetools.com