Yes the flatter the stock, the more recoil is transferred to the shoulder. The sharper the angle, the more rise on the barrel; it's a trade off.
I will look at that chamber modification, sounds fun. But the Mossin Negant is pretty crude, and may not be worth that much work. Restocking is easy, and would greatly improve it's looks and function!
I do like modifying these toys....
🤠💗😆