Seems the bottom line is: the stuffing should be safe to eat at the time you stuff the breast. Plus you're not stuffing a cavity. Chickens harbor salmonella in their guts, when they are degutted (which aint too carefully) the intestines tend to tear and release the bacteria. It gets into the tissue in the cavity. While the breast, thigh, whatever, might get into the safe zone the cavity might not making the stuffing, which is now also contaminated, unsafe to eat.