Found this thread where RC talked about stock repairs.
https://www.thehighroad.org/index.php?threads/03-stock-wrist-crack.305565/#post-3759113
Remembered the "hot stuff", also thought in another thread that Hobby Lobby possibly carried, but couldn't find that thread, I may be confused.
Hot stuff is very thin and best used in very tight cracks. Acraglass is a bit thicker resin and resists cracking a bit more. The first question is whether or not you still intend the fire the shotgun. If you do, I suggest getting a forearm just for shooting because cracking is a very common problem with these and fix the existing forend for prettiness and to retain collector/sentimental value.
Given the thinness of the wood here and the substantial recoil force the forearm is subjected to, cyanoacrylate (crazy glue) or even acraglass will fracture without mechanical reinforcement that tie the upper and lower section of the crack together. Either pins, bowties, reinforcement will have to be used to give any chance for success in a high stress area like this.
The CYA like hotstuff is usually pretty good about getting into tight cracks without much pumping to get good coverage in the crack. The thicker acraglass usually requires spreading the crack enough to get enough material in and then clamping it which forces the excess out (makes a mess so I recommend following Acraglass instructions using paste wax, surgical tubing, etc. to the letter.
On reinforcement, one way (which is obvious) is to carefully inset wood butterflies (looks like a bowtie) across the crack to hold it together along with the glue. Another way, that is a bit more promising in your case might be carefully drilling holes perpendicular (90 degrees) to the hole and inserting glued pin reinforcement such as threaded brass rods, wood dowels, even ridged nails or screws, etc. for reinforcement. On the perpendicular reinforcing pins, you want to have enough wood above and below to make it work. Depending on how you want it finished, you can either leave the brass tip of the pin exposed which will darken with time, or even use a plug to conceal it. Wood dowels are a bit easier to blend in to the existing wood. Obviously, the greatest risk is if the material shifts when drilling it and you go out the sidewall so you will need a drill press and vise for this repair.
Useful old THR post on subject
https://www.thehighroad.org/index.php?threads/wooden-stock-repair-question.643516/
Midway USA youtube on fixing a cracked Model 11 stock and forearm
Search out other repair tips from GunnyUSMC aka Candyman who used to do this quite a bit and explain the process on the THR and some other forums.
Example of a butterfly key repair and reinforcement. Used a lot in furniture repair. Usually pretty obvious repair so you want to be good at it. The idea behind using pins or dowels is not to be obvious--obviously.