There were no changes required in balenaOS for the wm8960 sound card to work - in that thread all the work revolves around the audio block and the customization to make it work.
Unfortunately as you point out the user that implemented the application using the block has removed it from github, and to my knowledge we didn’t include any changes back to the audio block that is wm8960 specific.
The way I would approach this is just making the card work on a standard distro, and then just copy the ALSA configuration across to balenaOS. There is nothing custom about the way balenaOS configures audio.