I can only remember the testimonial Ron Harris had on 23 November 1971, which was against the mighty Rangers! The official attendance was given as 16,362, but I'm sure that the true figure was quite a bit higher - Rangers brought thousands down with them, and it was a good atmosphere. I remember it well, it was the first time I ever saw Rangers play! Both clubs put out full strength teams, and Rangers won 1-0 with a goal by the great Sandy Jardine.
Obviously that's not the one you're thinking of, so I had a look in my copy of Ron Hockings' book of Chelsea history. Only game I could find was Ron Harris' second testimonial on 21 April 1980 (players got a testimonial after ten years service at a club). It was Chelsea Present v Chelsea Past , played at the Bridge in front of just 7,760 people. I know I didn't go, which was unusual, I used to go to all the games. Maybe I was saving my dosh, cos I know I went to Swansea away five days later!
Teams in the testimonial looked interesting: -
Present -
Bob Iles (Tommy Langley*), Gary Chivers, John Sparrow, Jimmy Clare, Mickey Nutton (Bobby Gould), Colin Pates, Ian Britton, Mike Fillery, Tommy Langley (Gary Johnson), Colin Lee, Chris Sulley (Peter Rhoades Brown)
* - maybe Tommy Langley went in goal when Gary Johnson came on?
Past -
Peter Bonetti (Tommy Hughes), David Webb, Allan Harris (Tommy Baldwin), Ron Harris, John Dempsey, Graham Wilkins, Ian Botham (Pat Holland), Mickey Droy, George Graham (S.Miller), Ray Wilkins (Jimmy Greaves), Peter Osgood (Bobby Tambling), Ian Hutchinson (Bill Garner)
Jimmy Greaves scored the only goal of the game, not bad considering he must have been about 75 at the time
Don't know where you got the Leyton Orient connection from - why would they play a testimonial for Chopper at Orient? Maybe you're getting a confused flashback - we won 7-3 at Orient earlier that season!