OK I solved the problem but I still can't explain why it happened.
I was determined to look for the simple things so I decided to re-chack the gap on the new plugs I had installed while trying to slove this problem. The misfires were at idle and slightly at part throttle with the old spark plugs and also the new colder plugs.
When I pulled out the latest plugs tonight, they looked pretty nice. But I noticed that the ground electrode completely covered the core. I had been reading about side-gapping plugs in Grumpy's thread, so I decided to try it.
I bent the ground tab up about 45 degrees, ground it about half way down on the bench grinder. Cleaned up the end with a small file and re-gapped them. Now the spark is going to have nice exposure to the combustion chamber. I installed them, crossed my fingers and fired up the car. Wow. Smooth idle, no missing but, as the car warmed up, the idled settled a bit low. I drove it, SUPER smooth power, and I came back and leaned out to idle mix from 10:1 to about 12.3:1 and it idles nice and smoothly.
Hmm.
This is NO B.S. Side gapping works!
http://performanceunlimited.com/documents/plugsidegapping.html
My Alfa Romeo used to use Golden Lodge spark plugs that had four side gaps! This was factory spec for Alfa in 1972!