just dropping lunch crumbs over a catalogue for Litchfield Engineering P/L, Croydon Park , SA Part no E3324 11/16" suits Ford OHV motor. These were made in Adelaide, so could likely be an abundance of them near Silverbullet around fleas markets, garage sales, swap meets etc. Save self grief looking for them in phone book or 'net. Cattledog is a bit musty and dusty - from 1970 !
Another tool that looks like it may also do the job is like an 11/16" ring spanner, that instead of a handle leading to other end, is a stumby number like two 20c pieces side by side, the second being 1/2" drive hole once again, part # E3344 another specialty tool to suit Holden EJ Sweephead
The one I borrow is a Sidchrome made tool and is structured more like the tool at most left,
, and was ground down a little to fit EA81 #1 head stud nut


11/16" = 17.4625 millimetres