One of these Black Apaches was my first gun. Great memories.
I would try Qbond on that stock with these steps.
first though, watch a few videos on youtube to get an idea what it is.
1. remove barrel from action
2. test qbond in a non-important area of the stock. if it bonds well to the surface, you're good to proceed.
3. clamp parts together
4. tape off areas you don't want to have glue on them.
5. drop in the Qbond glue from inside the stock.
6. sprinkle on a light layer of the powder from the inside and let cure for a minute.
7. repeat last step a bunch of times until the thickness of the layer applied is at least as thick as the break, all around the break. I would use all the powder in the kit on it.
By applying many light layers over a wide area, you should have an incredibly strong repair that is virtually un-noticeable to the eye, since all the glue is inside the stock. You'll also add a few ounces of weight to the gun.
8. This stuff cures as hard as rock, so don't get it in the area occupied by the barrel.
I really like using this glue and have found it to work as advertised. The layers of hardened powder become the strong part of the joint. You didn't have to fix the joint of the crack at all.
Canadian tire carries this glue for $20.
On the other hand....
this review didn't include qbond, but raves about JB Plastiweld. This should also work as they did test it on nylon with great results.
http://info.craftechind.com/blog/bid/323475/Stick-to-it-A-Guide-to-the-Best-Glue-for-Plastic
good luck with whatever you decide