I suggest you to be extra cautious about cross-flashing.
S801AB and AC are two different CPU although they are almost identical structure wise speaking.
What might really happen if you cross flash is that ROMs for AB doesn't have a proper CPU scheduler for AC. I am talking about the voltage input for CPU. You might very likely be running AC (0.8V required) with AB's voltage (1.0V). Sure, your CPU can take this little voltage surplus but in the long run this is no different than chronic suicide. The best way to get a proper ROM is to request for one that is made specifically for AC variance. Or, if I had to guess, keeping your stock kernel might do the trick here.
All in all, be very careful.