Welcome.
There is a policy that requests posters to contribute cash or posts before posting a For Sale ad. As implemented that also applies to posting Want To Buy as well. So you couldn't have posted in WTB until your post count increased even if you had wanted. 4 more posts and you want need a mod's help
There is a lot of anecdotal experience that says new, Newark Street parts do not fit vintage instruments and that the current Guild ownership rarely has the sight answer for anything Guild did before 2010. So in this case you actually got the right answer from Guild.
Ken Nash
http://www.theguitarmechanic.com/ worked for Guild and has a stash of old parts. You might check with him. But you may have to accept a substitute or pay the Big Bucks.
The mini-toggle is a phase switch. The S-100's bass brother, the JS, seemed to change specs monthly during 1970 and didn't really stabilize until 1971 so the absence does suggest '70 or early '71 to me. A serial number and more pictures would get you a better opinion than mine