Here's an article about it:
https://groups.google.com/d/msg/alt....M/CC8ksfp5RmUJ
It was about 600 tickets sold (the remainder of capacity was probably reserved for band guests). The show was announced on the radio at 7 PM the night of the concert, sold out in 20 min, and proceeds went to charity. According to the article, private rehearsals at the Odeon were the day before and day of the concert.