What I ended up doing was basically this:
1. vanilla buster install
2. update all the things (apt update ; apt upgrade)
3. add snd-soc-tlv320aic32x4-i2c and ax25 to /etc/modules
4. add dtoverlay=draws,alsaname=udrc and dtparam=audio=on to /boot/config.txt
5. install ax25, gpsd, hamlib, and related dev packages with apt
6. compile/install dire wolf from source
The hardware is working (gps confirmed, radio interface not yet confirmed), and I'm still working on getting the ax25 stuff configured and direwolf wired up correctly, but I think the hardware is functional now, as I'm seeing the sound card and the gps is working great.
Thanks again for your help!