I have finished the wedges at each end of the beam and the whole thing screws up really tightly and feels quite firm. The three spars slot in fine, but with little spare length for the boom. The shroud shackles on the mast just touch the mizzen mast when stowed, which is a shame. Just another millimetre apart and they wouldn't have touched at all. I don't think it will be a problem.
I have bolted on the tabernacle support. I had to widen the boom slot slightly as the goose neck fitting has to fit in as well. everything is quite firm. I am going to fit bungee hold down cords, which will be all that is needed to hold things in place.
You can see the wedges at each end. I am going to cut off the beam beyond each wedge and epoxy on a mahogany end cap. I have also drilled through the beam for navigation light fittings. I had thought I would have to level up the ends for the lights, but they are so close to horizontal that I don't think I need to. The boat will be rolling and heeling anyway.