Just to emphasise how silly the Rosemary Willis argument is.
Altgens6 shows Ready, Landis and Hickey all looking over their right shoulders, back towards the TSBD building.
This picture is thought to be the equivalent of z255:
Landis - "I heard what sounded like the report of a high-powered rifle from behind me, over my right shoulder...", "My first glance was at the President, as I was practically looking in his direction anyway...", "I immediately returned my gaze, over my right shoulder."
Ready - "I heard what appeared to be fire crackers going off from my position. I immediately turned to my right rear trying to locate the source but was not able to determine the exact location."
Hickey - "I heard what seemed to me that a firecracker exploded to the right and rear. I stood partially up and turned to the rear to see if I could observe anything. "All three describe the situation recorded in Altgen 6, their immediate response to the first shot.
However, when we look at the Z-film, we can see Rosemary Willis running along side the motorcade at the same time we can see the car full of Secret Service agents. We are being asked to believe that the little girl is reacting to the first shot when a car full of Secret Service agents make no meaningful reaction:

Altgens 6 corroborates the statements of the three agents, that they immediately look to their right rear, towards the TSBD building, as a result of the first shot. This shot was described as "ear-splitting" and an "explosion". It was heard all over Dealey Plaza.
The Rosemary Willis argument is a really desperate attempt to have an early first shot.
The Head Turn argument is equally as desperate. It's a motorcade, of course the heads of the limo occupants are turning.