“They had no opening act”
No, they didn’t...now that you mention it.
Tickets back then for Zep 1977 were Mail Order, With Bank Check or Money Order limit 4 per order, include an envelope for Tickets, or returned check. as Ticketmaster & Box had proved to be a nightmare in 1975.
I lived in NW Ohio at the time. My friends and put in orders for Cleveland, Cincy, Detroit, & Chicago and got nothing but our checks returned to us.
I did see Page/Plant and Jimmy 6 times