I think his thesis is that Kennedy's neck shot came through the windshield, but the fatal head shot came from the driver (Greer). And that Connally's wounds came from the rear, plus there was a shooter behind the knoll fence just as a distraction. However, I'm not sure what he thinks caused the second purported hole in the windshield.
Just imagine this conspiracy being planned. They set up a shooter somewhere near the triple-underpass area (to shoot through the limo windshield!), which had quite a few spectators and no hiding area, plus Oswald as the patsy in the TSBD, plus a someone with a gun behind the fence, and then they have the driver of the limo, in front of hundreds of people, pull out a gun and shoot him from the front seat, just a very few feet from the four other people in the limo, without them noticing either. I'm sure someone here could put together an entertaining transcript of the planning meeting which put that whole thing together.
In other words, 7f, your ideas are just nuts.