I downloaded the zip file for the 100a firmware and installed it on an SD card. It boots up and I can switch to ALT mode and navigate through the CHDK menus. It's been at least 5 years since I used CHDK, so I've mostly forgotten how to use it. The battery on that camera is also in pretty bad shape, so I need to stop and recharge it fairly often (including right now). It may take me a while, but I'll try to work my way through the features in the manual to see that things function properly. I encourage anyone else with this camera to test, as well, because I may not get done for many days.
I had given up on ever seeing this camera supported by CHDK, so I'm pleasantly surprised to see a port for it. Many thanks to
@blackhole for putting in the work.