Well, the true ground point should be at the output of the unit. Now for a PCB, one could have that at pin 7, for a unit in a box with e.g. binding posts, things look different. It should be at the negative output binding post. It needs to be set in a way that the change in current through the related wire from pin 7 to the output (load effects, temperature changes / related copper wire drifts and current accross) is sufficently low. The output impedance of a 732B e.g. is 0.1mOhm, as a side comment. So 10mA load at the output causes 1ppm change in voltage. It musst be assured, if that e.g. is the goal, that any return current from that binding post to pin 7 is not generating a ground shift.
The filter capacitor should be a lowest leakage foil capacitor, and the input resistor could be higher, provided the bias current (change again) of the opamp is low, the capacitor will anyway filter resistor noise.