Rotary gaps -- machine work


I've been working on a rotary gap for a while now (5 minutes at a time).  
The problem I'm having is making the disc run true.  The disc consists of 
two aluminum hubs with a 1/2" thick x 12" dia. disc of G-10 epoxy 

After reworking the hubs, they are sitting in the 3 jaw chuck.  A dial 
gauge shows that they have been faced so that there is much less than 
0.001" runout(?).  I then put the disc on the faced hub and put the dial 
gauge on it.  It shows about 0.002" at the center, and about 0.020" or 
more out of true at the edge.  Looking at the motion of the dial, I can 
see that the disc isn't just out of true, but is actually slightly warped 
or something. The needle indicates one "major" high point, and one 
"minor" high point.  These high points are not 180 degrees apart either.

After a little shimming, I can get things a little better, but not good 

This leads me to the reason for the posting.  How to true up the darn 
thing?  The three ideas that I have are 
1) Face the G-10.  I don't like this too much because it may weaken, or 
   at least make it all fuzzy.

2) Build up a rim of epoxy on both sides and face that.

3) Ignore the out of true on the disc, put on my brass acorn nut 
   electrodes, and face the points of them.

Does anyone have any thoughts or suggestions?