Triumph Of Mystery Lost To History

Scored this great little book from Franz and Grubb a week or so ago, it's full of really useful information that is as relevant today as it was when it was first published in 1968.

This picture appears on page 72 with no more information than that seen in this scan. Searching Google reveals nothing other than one other picture that is shown below.

It seems amazing that such a major piece of modification and ingenuity has somehow been lost to the mists of time, unless anybody out there knows any more.