Not sure what you are asking. The internal circuit of AD629 essentially simple (did you review the datasheet at all?), but when implementing it with discrete resistors it's very difficult to achieve a similar common mode rejection because you most likely fail to reproduce the resistor matching inside AD629.
So first question would be about your specification, particularly common mode rejection, but also offset and offset drift.
Depending on the nature of the high voltage (is it constant DC or varying, in the latter case how fast, any superimposed common mode AC?), there may be other level shifting solutions.