Its hard to tell from the pictures but those dark spots on the top of the wrist may be covering pins or something that has already been inserted, just guessing.
Personally I would strip it completely down and wiggle it until the old repair came apart (I doubt you could make the old repair worse) I would then scrape out any old glue etc. that was holding the stock from matching up with the smallest gap in the crack possible.
After getting the two pieces to match up as exactly as possible I would either use tite-bond or similar wood glue if I could get down to the wood in the crack, if there were still quite a bit of old glue present I would use epoxy instead of the wood glue and make sure BEFORE applying either one that I could press the two pieces together very tightly while they hardened.
After this set up I would drill through the joint at at least two different angles hopefully starting under the trigger guard if possible to hide the holes and without drilling all the way through to the top of the wrist and then epoxy in some small but hard threaded rod (cut the heads off some hardened bolts if necessary).
Depending on the final appearance of the repair I would either stain the stock very dark to hide the crack, or if it was still very apparent either wire or sheet metal wrap it and then antique it to appear as an old repair.
The main thing is to not rush things, this repair will take several days if done correctly.