Were all mast platforms planked one direction, I see some change direction in the center. Maybe it’s a Country or time period thing, it’s too late now, the platforms are all planked.
the print shows the top of that mast going back round to fit in the mast cap. The hole gets covered, so I may just file a square hole in this mast Cap.
a buddy makes pens on a little lathe, that lathe would be the ticket for rounding these dowels. Maybe?