Jason,
I have linked your great idea to use in the ARM7024 from Futurelec here: http://en.mikrocontroller.net/topic/116189. This will do well for low frequencies this uCntrl will resolve well.
If I keep the ARM7024's 3 Phase PWM at 50% duty-cycle, and use this excellent RC-timer circuit...
Jason,
How about adding a 100K Ohm Pot' in series with that 10K Ohm Pot'? That should increase Phase Adjust Range to 11uS while retaining the 1nS Phase Resolution you found in your experiment. Just a thought.
Ward