Finally, I was able to take those three boxes of books to my local used book shop. They took them all, and I have a nice chunk of store credit to use at my leisure. Whew! I did miss the deadline set by Clutter Buddy, but she let me slide due to little Jack's illness (and the resulting lack of schedule flexibility).
I do still have that pile of donations pictured below. I've been adding to it, and will drop it off today or tomorrow at my local thrift store.