Note there are a few variations of these 5-digit panel meters. Look at the pics before buying.
One uses a "22 bit" A/D SOIC-16 marked "BX5815" possibly a remarked Titan Micro TM7707 or 16-bit TM7705, delta-sigma.
The other variant another uses SOT23-6 for the A/D, possibly MCP3421.
The voltmeters come in 3-wire or 4-wire versions.
I think the ammeter's shunt looks suspicious with lots of copper colour, so I'm not sure how that alloy drifts with temperature.