There are three noteworthy elements in CBS journalist Dan Rather's 11/25/1963 description of the Zapruder film, all of which indicate that the film we now have is not the original.
1. When the current Zapruder film was made public, Dan Rather took a lot of flack for his 12/25/1963 description of the Zapruder film because he said that the head shot caused Kennedy's head "to move violently forward." But Rather might well have been telling the truth. Rather was not the only one who saw the original Zapruder film who said it showed the head shot clearly knocking Kennedy forward. Hoover aide Cartha DeLoach saw the original film on 11/23/1963, the day after the shooting, and he said in his memoir that the film showed JFK "pitching suddenly forward."
Also, several Dealey Plaza witnesses said the head shot knocked JFK markedly forward. Bill Newman tried to tell Jim Garrison that the head shot knocked Kennedy's head forward so hard that it looked like it had been hit by a baseball bat, but Garrison did not believe him because this event was no longer in the Zapruder film.
2. Another fascinating aspect of Dan Rather's account is his description of the separate hits on JFK and Connally. Rather said the film clearly showed that Kennedy was hit before Connally, and that Connally was hit only after he began to react to the shot that hit Kennedy. This agrees with Connally's emphatic recollection, and it even agrees with the altered Zapruder film. I suspect that the separate hits on JFK and Connally were much more apparent than they are in the current version, although they are fairly apparent in the current version. I suspect that the original version showed that more time elapsed between the hit on JFK and the hit on Connally.
3. Rather said that the film showed Kennedy's limo turning left from Houston Street onto Elm Street. Zapruder himself said he started filming as the limo was turning at Houston and Elm. This would have been a logical point at which to start filming. However, no such event is now seen in the film. In the current film, we see the motorcycles starting to turn left onto Elm Street but then the film skips ahead, and the next thing we see is the limo driving on Elm Street, starting at Z133; there is a noticeable gap between the motorcycles and the limo's first appearance at Z133.