looks like it was 1/2 drive and maybe more.
I cant seem to find a catalog for this one.
(https://c1.staticflickr.com/1/379/31615251293_b92ceb85e3_b.jpg) (https://flic.kr/p/QaJqKx)20170118_221644williams (https://flic.kr/p/QaJqKx) by Skip Albright (https://www.flickr.com/photos/skipskip/), on Flickr
My 1960 catalog does not list any S-320 sets, but all the Standard ones are 1/2 inch drive.