Factory antennas that I have seen on my 2 trucks were a single piece mast with a plastic fairing over the lower half. You should be able to buy a shorter mast to fit the factory base at Pep Boys or somewhere. I remove mine to put on a care cover for long term parking. Just pull up lightly on the plastic fairing and it will slide up the mast and expose the base. use a small crescent wrench to remove the mast from the base.
2003Excursion 4x4 Eddie Bauer 6.0
Edge Insight CTS, Autometer Fuel Pressure Gauge w/Strictly Diesel sending unit hose, ELC, Sinister Coolant Filter, F650 dash conversion, High Idle mod, Donahoe Racing 4.5" lift, LT315/75R16 Toyo Open Country MT, Viair, Salvaged oil-rig horn