The fuel tank I am using in my Cobra is built by the kit manufacturer especially to fit within the chassis of the kit. It comes with a hole pre-drilled for a VDO fuel-level sender. Most people use the height adjustable float/arm style sender, however the tank is quite shallow, and some people have reported issues of fuel-level-reading stability and fluctuations due to the fuel sloshing around in such a shallow tank. To combat this I am using a marine style tubular sender. This should provide a much more stable fuel level reading. The VDO tube type sender has the same fitting diameter as the arm type. In terms of electronic signal output the tubular sender operates the same as a float style sender, but they are made for boats which rock and roll across the water, so I'm banking on a very stable reading.
These tubular senders are not available in a height adjustable version, so you need one the correct length for your tank depth. They come in many different lengths. I am using the 170mm version of the sender, which will put the bottom of the sender about 3mm off the bottom of the tank - pretty much perfect.
Depending on your tank configuration you may need a fitting kit for the sender. Some fuel tanks have a welded in flange, and some have threaded holes for the sender to attach to. My tank has neither, so I need this flange fitting kit - note this does not come with the sender, and needs to be purchased as a seperate part. This flange is part number N05801432.