The mast has a solid plug inside the foot and the masthead to provide strength and for hardware fastenings.
Way back when I built the cockpit seatbacks I used some square section Douglas Fir to make blocking for the fittings in the seatback tops. That wood was in fact the blocking for the mast, so I had to purchase some more timber. Never mind ...
The plug for the top of the mast is 16" long and tapered on three sides, so quite tricky to make. I did it by cutting a piece 24" long to give me 8" to clamp in the vice while I planed it to shape, like this.
That worked well. The bottom plug is easy. It is 32" long and 1 1/2" square, so merely needs cutting to length.
Here are both finished plugs on the bench.
All the pieces of the mast are complete so next up is a test assembly.