What was your impression of the difficulty of three shots from a bolt-action rifle at a man-sized moving target from there?

You're asking a guy who's never discharged a firearm, let alone one with high power and a scope. I don't remember Oswald's qualification as a rifleman, and the closest one can get to his position (because of the glass enclosure) is the next window to the west...

But the X's on the street are clear to see from there (and the trees were smaller in 1963 -- in fact, Oliver Stone had them cut back for JFK, along with other temporary "historical restorations"). They also don't look all that far away. I suppose the limiting factors are the time needed to work the action between shots, and the speed of the motorcade ... but I seem to recall it was deemed possible at the time.