@LowNSlow - I am advised that the fuel gauge was from an MG.
Another issue if that the tank is relatively flat and shallow, making it harder to measure the fuel level accurately.
The best way to fly it is to fill the tank frequently and track the time flown.
I'm about to get Electronics International fuel level and pressure gauges fitted.
There are a few Airtourers around that have been wrecked and broken up for parts. If you fish around an engine mount should be available. Speak with the Airtourer co-op people.