Are you planning on redoing the whole car? From what I saw in your pictures,the body sits on top of the frame rails clear back beyond the door post,so to channel it you would have to redo the frame to pinch in the rails to allow the body to drop over them,or split and stretch the body out ? Why not Z the rails up 4 inches in the rear,and then only have to redo the floor in the rear. Just a thought, Hank