6500 at that match, but I'm guessing you couldn't tell how many Albion went up due to lack of segregation (and goals!)
http://thegoldstonewrap.com/2013/11/29/1973-brighton-0-4-walton-hersham-albions-worst-fa-cup-defeat/
That's a hidden gem! Was it a spelling test you missed, by any chance?:)