All through the 70's and 80's the Town End was indeed used for both home and away fans with little or no segregation. Sometimes a line of police separating the away fans if it was a large or volatile following.
Typically the away fans would be in the corner next to the Main Stand. IIRC They did finally fence that corner area off from the rest and it became the official 'away bit'.
Was in the RE on numerous occasions when the away team scored and parts of the RE erupted in song then violence. Particularly v Palace, Millwall etc. Different era.