There is a film here http://uk.youtube.com/watch?v=KFwmqaw7Av4&feature=rec-HM-fresh+div
that states in the information that it was Queen supporting Mott The Hoople at the Rainbow in March 1974. Queen only supported MTH in the UK in the winter of 1973 and in the US in the early summer of 1974 so if they did play the Rainbow in March 1974 it would have been as headliners. I can't find the information to check it though so please could somebody confirm?
honour one another and seek the common good