Been looking in to this, and it seems the issue with the A500 and overclocking the stock cpu, is that the "E-clock" signal that feeds other parts on the motherboard comes from the CPU, so if you double the speed of the cpu, this frequency also doubles.
However, the "E-clock" on the A600 is generated by the Gayle chip, so the E output from the CPU doesn't go anywhere, meaning if its the wrong frequency, it shouldn't matter.
BUT! I can't actually find any conclusive answer as to whether or not it will even work....
You can overclock a Sega Mega Drive using a 10Mhz crystal oscillator, feeding the signal into pin 15 (clock in) on the cpu, and this works fine on 99.9% of machines...
So, can this method potentially work on an A600? can I take the 14Mhz output from the Agnus chip and feed it into the 68000?