Reading other blogs it seemed apparent that holes needed to be drilled into the fuel tank aperture where the sender sits, conscious of not wanting any swarf to enter the tank, I expected the first job to be some careful drilling.
PA peasant and welcome surprise, the fuel tank had holes pre-drilled and threaded where the sender sits - well done GBS, nice "upgrade" on the construction of the fuel tank
So with the holes resolved it was a case of identifying the screws needed to secure - I established they are M5 x 10 and elected for the button head screw more for aesthetics rather than anything else.
Simple job, some thread lock onto each screw and secure the gasket between the fuel tank and sender unit with some gasket seal and tighten all up - job done.
One curious aspect with the wiring loom and the fuel sender wire, the wire has ring terminal connectors rather than spade connectors so they will need replacing to enable final fitment onto the sender - a bit puzzling this considering GBS supply the fuel sender, I would have expected common connections between the wiring and sender....