At long last the woodwork is done. I may have bought a bit too much balsa for this job... no doubt it'll find a use in the future.
Balancing time - it was good to see them joined again. It took about 2.7g (3/32 oz) on the starboard wingtip to balance - not bad considering the extensive reconstruction of the port wing.
I marked the position of the weights on the wingtip and roughed it out with a dremel and router attachment. I cleaned it up and enlarged it with a chisel.
After a test fit, some 30 minute epoxy went into the pocket, followed by the weights.
After the epoxy cures I'll cover the weights with filler.