I usually don't post on the forum but feel that I have to rely to this one to share information about these recordings.
The 1968 recording of the original cast of The Dream is preserved by the Jerome Robbins Dance division at the Library of Performing Arts (LPA) of New York Public Library at Lincoln Center, New York. It's not digitalised yet and I had to seek LPA staff's help in finding the recording and playing it. The tape can only be watched once at one time, because to watch it again it has to be rewound by the staff and the rewinding usually takes 15 to 20 minutes. The performance was inexplicably beautiful, almost magical. Sibley and Dowell were so wonderful together. I have to say nobody can ever hold a candle to them in these two roles.
And I think they also have the recording of Symphonic Variations here: https://digitalcollections.nypl.org/items/87437fd0-4b52-0133-4044-60f81dd2b63c . It's been digitalised, so one doesn't need the staff's help to watch it. However it can only be viewed onsite on one of the computers at the Jerome Robbins Dance Division of LPA. I haven't checked it out yet but judging from the cast information listed on the page, it is the recording you mentioned.
I'm now living in New York. Since discovering the archive that LPA had a couple of months ago I have paid several visits to it and had the chance to find a few hidden gems there: Act IV of La Bayadere by Fonteyn and Nureyev, Clips of Giselle by Fonteyn and Nureyev with Sibley and Shaw dancing the Peasant PDD, Sibley&Dowell&Seymour&Nureyev in balcony PDD in a promotion video of Romeo&Juliet, etc. There is a lot more to explore and I'm so grateful that NYPL has made an effort in preserving these recordings. I hope one day they will be able to digitalise all of them (right now they're short of funds as far as I know, so the digitalisation has been very slow).