The patchbox recess will determine. First, long pieces of all thread, see drawing. The brownells brass kind is great. I also use 6-32 all thread from the hardware store. Pre-drill with an aircraft length bit, and fill the length of it with epoxy and the rod. The butplate and toe plate can cover the rods.
Second is to insert a slab of maple with the grain oriented up and down. A morticing or horizontal boring machine will be helpful to remove the material. IF you run into the patch in the bottom of the patch box it will not be as big a deal as the all thread.
Does the crack run through the patch box recess? For thin areas that break I have used perforated plates of steel or brass with many small holes. Bed it in epoxy. It may be possible to insert that in the bottom of the patchbox and cover it with a thin piece of maple.
Pictures are needed. I am wondering about the grain layout. It may be such that the toe is very weak.