I am not at all familiar with a Fausti, or what it might take to cheat and adapt a Winchester 23 stock to fit. But you are correct to think that recoil is likely to crack thin sections. Ideally, the more surface area of dense end grain that you can get inletting contact with on the rear of the action, the better. The only place to avoid contact is where a wedge effect might split the stock, as at the rear of a tang for example.
I have seen where a gunsmith built up thin or weak areas in the inletting, where it wouldn't be visible, with small blocks of walnut epoxied in place. Then this added walnut filler block is headed up as if you were starting from a blank. Sounds like good practice if you can pull it off.
