the Patent for the slant pantograph was SunTour's, until it expired, now it is pretty universally adopted by everyone .

One workaround while the patent was in force was The A-B switchable angle Chorus .. I have one of those . (sell?)

I had it on a 1 by 6 with a 13-34t freewheel .. it's short chain cage rotated around its guide pulley axis ..

a double would need more wrap up capacity..