Well, Grumpy, you were right! I had already removed the screws but the panel would not come "out" of the cabinet/mount. Then, this evening, as luck would have it, my wife came to see what I was doing. She said, casually, "You know, if you took this hardwood trim strip off the slideout frame, that microwave would come right out."
I scoffed. Then I checked the trim strip and saw it had been removed before. Soooooo, I pulled it off and the microwave came right out.
This post automatic power transfer switch work is hanging on a long time.
Thanks to all for the help!