An '89 has an aluminum mast with only an anchor light and associated wiring. Any decent welder with a tig could remove a foot of mast and weld the anchor light fixture back on. Most of the GB aluminum masts are hinged at the bottom. The mast could be lowered enough to give you the clearance you require without the technical details of lowering it all the way to horizontal.
I'd start by carefully measuring the current height. Perhaps a previous owner chopped it already!