Funny ... I didn't have this show in my spreadsheet, came across it and wrote a post, only to see that it's listed at Deadlists and boasts a gorgeous Miller sbd over at the LMA.
I guess all I can salvage is that tickets were still available as of the day of the show (1).
(1) George Anderson, "Stage and Screen: Valdez is Coming at Gateway," Pittsburgh Post-Gazette, April 12, 1971, p. 22. Accessed via Google News.