No, I have Hooker Long tubes in my '73 Mach 1 with a 351C 4V and a drop bracket was not required. If you can't get your car at least 3 feet above the ground during install, you might have to pull the pitman arm and unbolt the steering box to move it out of the way temporarilly, but that's all.
Just FYI - 1971-73 Mustangs have the power steering integrated into the steering box. There isn't a need for a drop bracket because there isn't any slave cylinder under there.