Saw this on the U-TUBE. Why they don't include all of this stuff when they re-release movies on dvd, blu-ray is beyond me. This guy went to an event where they played the screen tests for Crispin and Lea - no sound but very interesting. This is part 1 - part 2 is up as well.
YouTube - Rare Back to the Future Screen Test
On a side note - I was reading an old interview with Robert Z talking about how in real life the Delorean was always breaking down on the set and something it did in the movie as well. He went on to say (while filming part 3) that originally there was a scene written where Doc and Marty go to pick up the car from Downtown Hill Valley - at the end of part 1 after Marty returns from 1955 and Doc shows him the bullet proof vest, Doc reveals a kill switch he had installed under the car's dashboard - but Zemeckis said - "if I'd thought about it sooner and planned on a sequel and knew I would be returning to 1955 - I would have timed it to have the original Delorean effected by the fact that it was in two places at the same time - when the flying car traveled back to 1955 it would cause Car A to sputter out for a moment. It would have fun to try and sync those together and give that as an explanation. I'm not saying we could have pulled it off - but it would have been fun to try."