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I'm loving your detail shots tho' - they'll probably be enough to tip me over the edge.
For the beam I would go with a steel plate cut to profile, drill for and solder in bosses for all the pivots and also solder on two steel strips for the top and bottom flanges, all done with silver solder.Then run the moulding in brass, bend and soft solder in place. Bit hard to tell is it a convex quadrant moulding or a concave scotia moulding? If its concave then maybe cut a tube into 4 quadrants. The other way is to use a roundover or bull nose cutter depending on shape to cut the profile on the edge of a flat strip so its easy to hold and then cut it off with a slitting saw.
Be warned I have about 150 of these as well as a full set of Anthony Mounts drawings that I have hand corrected from measuring our engine. Anthony is also looking forward to seeing this one built.
The brass would have to be very soft. It might be worth an experiment, it is not as if it would cost much .Jo