Hi dclm
Right, I missed that load cell was excited with +10V only. Then the negative supply doesn't matter.
However normally you supply load-cells with symmetric supplies so the output signals are close to 0V.
This is to minimize the effect of leakage current signal to zero/ground.
With an inamp of gain 1000, the internal signal levels in the inamp must be studied carefully.
3.8kg makes 7.6mV. It is amplified to 7.6V and the common mode input is 5V. Then the internal voltages goes to 5 + 3.8 = 8.8V. (Eg. the upper voltage over R1 inside the AD620). Make sure there is room for this in the amp.
The alternatives can be similar but the influence of the filter gain drifts will be a little higher in case 2.