If the podcast doesn’t exist anymore I think the best way would be with using local folders and adding them to AntennaPod.
It will show the same as if it was a podcast. For podcast main image I think there is a way to add one in your folder to be used as a cover but I don’t know how to.
There is another thread not too old on this forum where somebody asked for that and it was possible. Found it : https://forum.antennapod.org/t/ability-to-display-podcast-image-for-local-folder-podcasts/486/2