I'm not sure they averaged the biggest home atendances that season. I'm sure Liverpool would have been higher than theirs was.
There is a very good reason why the Utd game it home in August 1974 has reached mythical proportions. Here are two reviews of that game, both from the Man Utd perspective. In the 2nd paragraph of the first article the writer states:
Our supporters would descend on the rival town or city and take it over. Trains, coaches, cars from all over Britain would arrive throughout matchday. Rival fans were overawed. There would be exceptions, some rival supporters decided to stand in the way of this Red tide. Cardiff City on a bright, sunny August day in 1974 were the first.
https://strettynews.com/2013/11/24/t...-39-years-ago/
The second contains descriptions of characters that a few of our older fans may recognise:
https://www.redcafe.net/threads/card...d-1974.158684/