Switched things around a bit. The Tacho, Speedo and Temp dials can be controlled through CANBUS - I changed direction and started using proper Mather through HEX byte values and achieved linear operation although the Speedo still has a “get no tickets” margin that’s probably all about the needle position.
My test harness gives me control of the Brake Fluid level warning and the back lights. Fuel and Ambient Temp are derived from resistors so I will have to read the manual and get some suitable.
For the moment this is all I need to do as the objective was to make a small piece of hardware that would allow quick calibration of the needles when reassembling the clusters.