JBC was a big man in a small seat and his movement was restricted when trying to make a normal turn. It was only after he received a severe gunshot wound that his severe gyrations in reaction to his wound turned him completely around in his seat.
He had no difficulty turning around before on Main St. to speak with JFK. Besides, the seat didn't prevent him from turning his head. The normal range of motion for rotation of the head is between 70 and 90 degrees. JBC's head is practically square to this shoulders.
As for Mary Woodward and all these other witnesses you site, the reason I have so little faith in them is because people only remember things well that they made a mental note of at the time. I see no reason to think Mary Woodward would have made a mental note of where JFK was at the time she heard the first shot. That's something she would have had to mentally reconstruct when asked about that later. At that point, she would have just been guessing. There's only one witness that didn't have that problem. Zapruder's camera. That is the witness I trust above all others. That is the witness I measure the credibility of all other witnesses against. If a human witness tells me one thing and the Z-film tells me something else I'm going with the Z-film every time.
You don't think that she would remember that JFK's turn in her direction and his smile and wave occurred just after her cheer? Or that it was before that first "horrible ear-shattering noise"? She mentioned it in her story she wrote as soon as she got back to the office that afternoon. She said that both he and Jackie turned and smiled and waved at them just after she shouted to them. She wrote that they were the last people the President ever acknowledged because as his car passed by them, he turned forward and the first horrible ear-shattering noise sounded.
We can see that the zfilm matches perfectly with what she described seeing. JFK turns from looking forward left to looking sharp right beginning at about z160. Starting at z172 JFK raises his right hand to wave in the direction of Woodward and her friends and Jackie starts turning from looking left to forward right at the same time. So we know that she accurately remembered JFK acknowledging them with his smile and wave. She just got mixed up thinking that it was before the first shot?