For some more info on the Phillips Auto Spark Control and the Nu-Rex see The Ford Garage;
http://www.fordgarage.com/pages/phillipsspark.htm
http://www.fordgarage.com/pages/nurexadvance.htm
There was another thread on Ford Barn but I can not seem to find it.
I do have a Nu-Rex on my car and I really like it. My initial timing is set retarded to limit total timing to 28° as Dave in MN suggested.