Joseph,

Many thanks for the advice.

I'll read the thread and source an adjustable proportioning valve.

I think you are right about the third under dash switch. When I turn the ignition on I can hear the fuel pump ticking, it goes a little quieter after 10 secs (fuel bowls full) but never actually stops. Obviously I need to flick the switch the other way at that point.

Turns out on closer inspection that one side of the two lower (smallest) leaves are broken completely off on both rear springs. I'll have to remove them and ship down the England where therer's a company (Jones Springs) that specialises in making classic car leaf springs. I'll drop the fuel tank at the same time to sort the vents and repaint behind.

Mark