In the far recesses of my memory, I seem to recall a drawing of this style flanger... RMC, long, long ago? I wonder if a search of the magazine index would bring up something? Boxcab E50
That might work... I dug a little, and came across Colorado RR Museum. Thair library might have something that would help. I emailed the request--we'll see what happens.
Hope this will work. Try: http://index.mrmag.com/tm.exe?opt=S&cmdtext=Flanger&output=3&sort=d Boxcab E50