I'm not following what your plans are, but I didn't intend to suggest that you glue the recoil plate to the stock. In fact, I wouldn't do that. There is no percentage in putting the SG on the flat of the shelf unless the wood is rotten and porous, which I doubt. I think we're talking about two different things. I thought you should fix those cracks on each side of the recoil plate shelf with the SG. Unless cracks radiate from the chip behind the tang of the plate, there's no reason to put SG there. The repair for that chip would be to cut it out to a specific shape and glue in a piece of wood. Normally the tang never hits the end of the relief if its tight. The marks inside the stock from the receiver hitting it are most likely from the same event(s) of firing grenades - very high power, but still less than the factory proof round. Possibly the plate was a little loose when this occurred, which is why it chipped the stock and let the receiver hit. If you use the SG in this manner, the idea is to let it cure for 24 hours before installing the plate. Then you would use bedding compound to hold the plate if it will not tighten up.
As mentioned by Frank and others, be aware of the possibility that the cracks extend to the plate screw bore. You can still use the SG, but you have to monitor the bore to see if any glue comes through. All you have to do if it does is to stop and let it cure for 15 minutes which will stop up the cracks and let you continue from the front. If SG gets into the threads of the ferrule, you will have to clean it out with Acetone - so it's not an emergency.
I was thinking that if you stabilized the shelf that the plate might be okay without bedding it in. Even if you do bed it, you should use release compound so it is not glued to the stock - it should be removable. You should be able to take it out of the stock with no tools after pulling the screw out, and put it back in without tools. Ideally, the fit should be such that there is no play with the screw out, but it is a part designed to be removable.