It is widely recorded that Tom O'Horgan was the second choice for the slot of director. Frank Corsaro was originally slated to direct, with Grover Dale providing choreography; both made arguably significant contributions (selecting the design team, casting many of the principals, asking for changes in the material that led to added lines in the "trial" scene and the number "Could We Start Again, Please") before Corsaro was injured in a car wreck, necessitating his immediate replacement.
According to Tim Rice's autobiography Oh What a Circus, HERSHY KAY was hired to futz with the orchestrations for Broadway, which did not particularly thrill Andrew Lloyd Webber to any extent, as he'd done the original orchestrations for the album and anticipated adapting his own work. The end result wound up being that Kay basically rehashed Webber's work, with the only real changes relating to the size of the Broadway orchestra compared to the resources available for the album, and so after a bit of wrangling, Webber retained sole credit for orchestrations.
Ovrtur is a database covering musical theatre from Broadway, London and beyond.