I am inclined to believe that they aimed the jet at a place where they thought it would do the most damage. Any passenger jet with fuel would do the job, I think, considering the mass times velocity. They wouldn't want to bounce off the top and it would be hard to get down low, I think.
A fireman talked about bombs planted in the building possibly or in the jet. One bystander said a bomb had gone off after the collision. I think they missed no opportunities to make this a major terrorist victory.
it is neigh well impossible to "aim" a 767 within 50 ft of a spot on a building..........unless one has 4,000 hours or so of flight time. IMHO, the guys who running the show were seeking to simply hit the dang thang