Well its pretty easy to be honesy, take the centre console out and the old guages just unscrew, my cheap "Dragon Sport" guages ( 52mm I believe they were) just fitted stright in with a bit of hot glue to fix them in place. all they need to work is an ignition live, Ground (I got both from the headunit) then
the green wire runs all the way to the sensor, you need to bear in mind that removing the OEM oil pressure sensor will dissable to oil pressure warning lamp on the dash an also might throw a code on the ECU and other possible issues. to get arround this you could use a brass t piece and still run
the oem oil pressure sensor, let me know if you get stuck with anything.
Thanks for the write-up, this is very useful. I'll sleep on it - what I was thinking was a bit more "orthogonal" change, leave the OEM sensors in place and with the sandwich plate just run two new sensors straight to the gauges.