The point of no return: Here I've begun removing material from neck using chisels. A secondary mortise is being fashioned, so I can introduce a maple block which will become the new tenon. The elastic provides radial pressure on the soft wood, thus discouraging cracking.
Dry-docking the neck and headstock, to illustrate the fit. The newly formed channel is ready to be fitted with the new wood.
Roughing-in the new block. I'll tweak this with the chisel until maximum surface contact is gained. Then it gets glued with dowel reinforcements.
The finished tenon. The final cut parallels the curve of the headstock, while the hole accomodates the tuning peg. Note the dowel reinforcement. 
After the final glue-up-the pieces are joined tight and straight. The headstock now vibrates as one with the body (a coupled system). Two more reinforcing dowels will be added.
Headstock. Contains half of the broken tenon.
