Different performance totals are given in different sources. The Best Plays of 1970-1971 lists a run of 351 performances, but Variety and Theatre World both reported 343. While most of the time we would be inclined to trust Variety and Theatre World over Best Plays, in this case Best Plays seems to be correct.
Some online sources report 6 previews, but that is incorrect. There were 14 previews, starting on October 28, 1970. There was originally to be only one Broadway preview, but the show opened was overlong at the time of the first tryout performance in New Haven. One contemporary stated that the first performance in New Haven ran four hours, but other reports placed it around three hours of performance time plus an intermission, and that seems to be correct. Much cutting and reworking was deemed necessary, especially after poor reviews greeted the Boston opening that followed New Haven.