You likely knew this. The Cowsills were supposed to be Partridge Family and the show is basically based on them. They had a contract dispute because the band wanted their mother Barbara cast as their mother since she was in the band. The producers had already casted Shirley Jones. They do have a live video singing "I really want to know you". This was long after Barbara had passed. Also passed were two of the brothers the oldest and a younger one who died in NOLA during Katrina. Here's a great version of Hair with alternate last verse.
https://www.youtube.com/watch?v=2Dn9Zn9Simc