Looking at these diagrams:
http://www.wa2fnq.com/fnq/amstrblk.htmIt looks like all it takes is the stereo sum to be delayed 90 degrees out of phase from the stereo difference, then the difference is phase modulated and the sum is amplitude modulated. I have read one place that mentions a 2nd harmonic component used to eliminate distortion.
http://users.hal-pc.org/~jsgil/AM-Stereo/ISB.TxtTo me, it looks like the Kahn system is identical to the Magnavox system, just add the phase shift on the sum and difference channels and drop the pilot tone.