> MPC7447A HW spec I read before overclocking. But I cannot find anywhere
> MPC7447B ;-) So for simplification I assumed, that only difference was
> higher Maximum Rated Core Frequency - maybe 1.5 - 1.67 GHz ;-)

I don't know what the specific difference is between 7447A and 7447B/C, but it's not the maximum rated core frequency as there have been 7447A chips rated at 1.7 GHz, like the MC7447AHX1700PC (see Freescale/NXP PDF linked there).