Back to the Future II was originally going to take Marty McFly to 1967 where he’d meet an acid-tripping , motorcycle-riding Doc Brown and his hippie parents. The entire script is available online.

"In the first draft, written by Gale and with the working title "Number Two", there were some elements that would appear in the final version released in 1989. As promised at the close of the first film, Doc, Marty and Jennifer traveled into the future to accomplish the mission ("Something’s got to be done about your kids!").

While in the year 2015, Marty spotted a sports almanac and was determined to bring it back to 1985 so that he could win bets. Biff stole the almanac and the time machine, and when the travelers returned to 1985, they returned to an alternate timeline where Biff was rich, powerful, and Marty’s stepfather. Leaving Jennifer behind, Doc and Marty went back to the day that old Biff gave the almanac to his younger self. Instead of revisiting 1955, however the script called for Doc and Marty to travel to September 20, 1967.

Out of place in 1967, Marty ends up in jail. Lorraine posts his $500 bond and cancels her plans for a romantic weekend with George in San Francisco. Marty realizes that his birthdate is nine months away and that he has, once again, endangered his existence.

No provision was made for a third film. The draft closes with Dr. Brown’s advice to Marty that his future hasn’t yet been written."