First of all, the cake was delicious. The recipe served many people, and it's all gone.
However, the middle sank. So I should have listened to EMDB and ciaolette, who thought the large amount of baking soda and powder was needed for that much flour, sour cream, etc. My compromise helped a bit, but not enough.
Next time I'll make Nancy Berry's recipe and not worry about it.
I can't tell you how much I appreciated the people who gave me prompt advice. This Board is really wonderful. It makes one feel not alone in the middle of a crisis!