Maybe someone cut the mast shorter after breaking out the mast base?

The extrusion should be 18' 3 3/4 inches from the base of the extrusion (not including the base casting) to just above the mast tang. That is the cut length when installing a CompTip.

Another thought is to check the forward crossbar bend and then the height of the tramp / frame including forward crossbar over the hulls. Maybe a pylon is shoved down in a hull? Crossbar is flatter? Something that brings the mast lower than designed?