My factory grips fit fine in the area you have shown, but required sanding near the screw on the right inside. Other posts in this forum address grip cracking also. One member fixed his with cyanoacrylate (CA) glue. Something I didn't know could be done. Web research discovered wood pen crafters use it for finishing and strengthening their wood blanks. I chose Starbond EM-02. Their claim was deep penetration, due to its viscosity just above water. I finished my grips with 3 coats front and back sides. My grips did not crack at assembly, but I have not been to the range to torture test.
You apply thin coats with your finger. HINT: use disposable nitrile gloves. I kind of found out after beginning, that body moisture on your fingers accelerates the curing process.
