Nice looking rifle you have there... Not sure about the two screws, there isn't anything that they would screw into where they are. I'm assuming that they are wood screws not machine screws and that there isn't a nut on the opposite side of the stock.
I have seen some folks think that they are stopping a crack from spreading by drilling a hole and/or inserting a screw in the drilled out hole but never in a rifle stock.
they are wood screws and I think someone did it to "stop cracks" too. I've seen this before on older guns but assumed, like you, that they were to stop cracks. Just thought I'd see if anybody had some insight and had a different answer.
And yes, it is a great gun! The bore is shot out, the wood is cracked, the metal isn't the best... but i love it! I plan on getting the barrel relined this summer and hope to make her a shooter.
If you look real close from either the top of bottom of the grip, is there any evidence of a vertical crack? Probably starting at the rear of the upper or lower tang. If not there, possibly under the tang and not visible without removing the stock. I really doubt anyone would stick screws through their rifle stock purely as a preventive measure. I'd bet that at some point, there was a visible crack and they put the screws there as a repair. Probably put glue in the crack too which might make it real hard to see if they got it drawn closed real good with the screws.