Well you could add 560 ohms in series with the output, change R6 to 150k, C1 to 560pF,
but then you'd have a -6dB attenuator into 600 ohms.
Buffers are low output impedance so the the voltage gain is unity whatever the load.
You'd need a different circuit to get x2 voltage gain suitable for driving a 600 ohm output resistor into 600 ohm load.
