Wheelspk

For anyone following here, I've been talking to Wheelspk on Facebook, where he also posted the same questions.
From that log, I've suggested the following:

Do it in volts as I said.  You can temporarily set the analog input function to "voltage 0-5V" and the ecu will tell you the voltage, you do not need to measure it with a standalone tool.  Fill the tank from empty in some regular volume increment and note the voltage at each volume.     

Provided the level sensors are 2 wire, then wire them in series, you will then get the average of both sensors. 

 
 For the setup, set the analog input as a GP input, probably cal 7/8/9/10 is the most suitable, Volts vs %.  Empty tank, check the voltage on ANVolt, this is your 0% voltage to input into the cal table axis (my example below is 0.6volt for 0% full).  Repeat for other increments such as 25%, 50% etc.  You could just do 2 points calibration (empty and full) but it will unlikely be accurate in between.
 

It will need to be wired to an analog input and you will need to build a pull-up and filter circuit to slow the signal down so you dont just see the fuel sloshing around.

 
 

Forget what the Mitsubishi manual says about 13%, that's only relevant to the original ECU, the Link reads 0-100%, and you calibrate it to your current TPS position.
You could still do the Idle Position Switch way of setting the TPS (if, for some reason, you thought you might be putting the stock ECU back in), but so long as the Link sees a varying voltage from rest to 100% open, you're good.