Attacking target at 64 Mhz

Hi all,

I am trying to attack a board that runs at 64Mhz. The issue is that the board does not allow to modify the cpu clock nor access the internal clock.

So far I output an 8 Mhz signal for the target, it is generated with a timer and used for the ADC clock. I do the sampling with ext_x4 at 32Mhz.

I would like to ask you if this can be considered a correct way to synchronize?
If synchronized sampling can overcome a 50% undersampling?
Can used the signal generated with the CW in the place of a crystal?

Thanks in advance.