If you run both of the 8051 off of the same clock signal, but invert the clock signal to one of the 8051's , you shouldn't need to look for a "busy" signal. You would guarantee that you would not get a read at the same time that location is being written.
Wrong, !RD might start 1/2 clock cycle after !WR and both pulses are wider than 1/2 clock cycle.

Erik