I marked out and shaped the narrow mast spars tonight. I was going to use the router to shape it but by the time I'd 'jigged' it up with guides and clamps it would have been a week next Tuesday.
In the end I just marked it out with pencil, clamped both narrow faces together and power-planed them both together. Seems to have worked out pretty well. Very hard working with timber over 5m in length.
The timber is finger jointed pine of some type (radiata, I guess). Cheap and relatively nasty, so it will be interesting to see how it stands up to serious use. Hope I'm not wasting my time.