Further to my post #56, I ended up using an LTC2054 AZ opamp with 640x gain as a simple preamp to the galvanometer in a vintage PYE 7440/G wheatstone bridge. This effectively gave a net gain of 10x to the null display, as I wanted to drive the combined meter and Ayrton-Mather damping network to maintain needle damping (and that imposes a 64x attenuation). I can now easily discern sub 1 ohm step changes for a bridge measurement of 10kohm with 12Vdc bridge supply, whereas before it took about a 5-10 ohm step to see a discernable needle movement (unless I used a significantly higher than 12Vdc bridge supply).
It is a neat upgrade that just needed a 5Vdc input barrel socket added to the top panel, as I was able to use the front panel switch contact for an external galvanometer to power the preamp and connect it into the meter circuit. I was able to use a 5Vdc USB power brick (a Sony CP-F2L) for powering the preamp - the brick does add 50mV transients each 240us (4kHz) on a 20mV base ramp, with some dither, but that was simply filtered with an RC and had no impact on opamp output. The only other aspect of using a brick is the need for a load to keep it connected - which for this brick was 390R, or 65mW.
The LTC2054 output was nulled to <1mV in an un-energised bridge, and when the preamp was on it just noticeably deflected the meter needle, which can be easily reset to mid-point if needed by the top panel manual meter 'set zero' adjustment, so no ongoing need to adjust bias/offset for time and temperature. I'm now a convert!