Several flights and 3 hours of flight time later:  Everything is working beautifully.  The plug fouling was definitely caused by the Permatex anti-seize.  The top plugs fouled first because of the straight threads on the plugs -- Think of all the pressure being on one side of the plug threads where they meet the hole threads and are torqued up against one another.  This leaves a spiral channel on the other side for the liquefied paste to travel down and coat the plug tips and insulation with aluminum/copper/graphite residue.  After all, the copper seal or, in the case of moped/auto plugs, the compressible seal is what keeps combustion gasses from leaking out at the plug base.  The bottom plug took a little longer for the goo to affect the plugs.

 

So...... If an anti-seize is to be used (and may be necessary for the proper torque), put it on two threads back from the tip and only on two threads.  Apply sparingly (not like me, I overdo everything except a rare steak on the grill).

 

I will never use the Permatex again.  I will use the Champion anti-seize as I have before but more sparingly.  BTW, it appears that lacquer thinner is the best way to cleanup the Permatex.  I will let everyone know if others at my airport are able to clean and re-use their Permatex fouled plugs.

 

Since I am using Denso Iridium plugs, I got the following info from their web site.  Note the statement at the end about "lubricants."  This is why Klaus recommends anti-seize and 15 ft-lbs for the plug - see the entry for 14mm Flat Seat below. 

 

Installation Key Points

1. The threaded area of the cylinder head must be clean.
2. Using your fingers, screw the spark plug into the cylinder head, and tighten about 1/4-1/2 turn with a plug wrench. (Taper seat plug: about 1/16 turn)
3. Tightening too much may cause distortion of the plug housing, and in extreme cases could cause engine damage. Therefore, proper installation of the spark plug is important for life and performance of the spark plug.

Plug Size Cast Iron Heads Aluminum Heads N*m lb-ft N*m lb-ft 10mm Flat Seat 10-15 7-11 10-15 7-11 12mm Flat Seat 15-25 11-18 15-25 11-18 14mm Flat Seat 35-40 26-30 20-30 15-22 14mm Taper Seat 9-20 7-15 9-20 7-15 18mm Flat Seat 43-52 32-38 38-46 28-34 18mm Taper Seat 20-27 15-20 20-27 15-20

Note: The installation torque values shown above apply to new spark plugs without lubricating the threads. If threads are lubricated, the torque value should be reduced by approximately 1/2 to avoid over-tightening.
* 1N*m = 0.1020 kgf*m