Okay, here’s what I did to get it working. I downloaded the latest marlin here: https://github.com/MarlinFirmware/Marlin. I opened the .ino in arduino and made the changes Ryan mentions here: https://www.vicious1.com/marlin-firmware/. I then enabled the LCD using a couple of the things listed here: http://reprap.org/wiki/RepRapDiscount_Smart_Controller (some of the items were already done, so I didn’t have to do them).
The LCD works fine, and I’ve been able to move my CNC on each axis using it.