I too was there that day (April 23rd, 1973) Fuck me, it's getting like the Sex Pistols at the Mucky Duck! I was sat in the north (Now Sir Alex Ferguson ) stand where it curved round to the yet-to-be-built Warwick Road end. The crowd was an (at the time) massive 55,035* and Wendy were at home to Carlisle in the third tier that day. 0-0. Crowd around 8k. Masseeve! According to
this, Tommy Docherty was Man. U's manager at the time. Bobby C. still had one more League game to come - away at Chelsea on 28th April. Before the game the BBC cameras for Match of the Day captured the Chelsea chairman handing Charlton a commemorative cigarette case (!). The Chelsea match ended in a 1-0 defeat. His final goal came a month earlier, on 31 March, in a 2-0 win at Southampton, also in the First Division.
Around 1992 or 3, I was doing an exhibition (street furniture, as you ask) at Old Trafford in the Stretford End. During a lull in proceedings, I blagged a trip into one of the exec. boxes. The vertiginous North Stand was being constructed and it towered over the other three sides. I asked a MUFC flunky if the plan was to raise the other three sides to the same level. He looked at me 'gone 'art' and said 'Don't be daft. That would make it around 75 thou capacity!'