Rang Minispares and they confirmed I have the injection sender in my tank, but it isn't a problem as either can be used on the carb version.
Before ordering one I thought I'd test the one I have. Ran the petrol down and removed it from the tank. Reconnected the wires and put it through its motions. When it reads empty on the guage, and when it's against the lower stop tab, there is still enough juice in the tank to be just below the sender aperture. When I moved it to the 'full' tab it reads 3/4 on the dial. So working but not very helpful. I put 2 very slight bends in the arm. One to allow the float to dip lower into the tank before the stop, and another to allow the arm to rotate more before it hits the full tab. When all put together the lower reading on the guage was now about 15 - 20% fuel remaining, instead of the previous empty. Nipped to the petrol shop and filled up with the missus watching the guage with the key turned. Stopped when full. Checked with cameras and it's just touching the neck. Only thing remaining now is to run it to red and hopefully not run out
There's an easier way.
Fill the tank to the brim, record the mileage (A).
Run it for 200+ miles. Note indication on gauge needle.
Refill the tank and record the number of litres it takes (C ) and the mileage (B)
Subtract the number of litres added © from the number the tank can hold (D). ***
Subtract mileage A from B and divide that number by C. That'll give you an average full consumption per litre (X).
Multiply X by D and that'll tell you how far you should be able to go on your, now, full tank (Z).
Add Z to B, write that figure on a post it note. Stick it next to your odometer and you should hit the red before you get to that mileage.
If you repeat the above process to the ***, it'll show how many litres, and therefore miles, you have left when it hits the red.
Easier to do than describe. 
Edited by Quinlan minor, 25 September 2024 - 01:30 AM.
