Hi Julian,
There's been discussion in threads before about twin tanks, plumbing etc. It can get intense because there are so many variables including packaging, surge tank (or not), size of fuel lines required, safe layout of all components, sevicability after completionand so on.
You are heading done the most challenging road of any GT40 build. I'm sure a lot of good information will be shared.
Having done a couple of EFI systems on CAVs, both work very well yet I'd still do it different next time. If I had the luxury of designing the entire system prior to build, I'd go with a balance pipe between the tanks, with a single pump and fuel pressure regulator located in a surge tank within one of the two tanks. Then you have no return lines, no switching valves, one pump, one fuel line output, no exposed surge tank, a huge saving in plumbing hardware and much tidier engine bay. Just my 2c worth.
Of course you have to work within the layout and major components in your car. With good planning and a few dry runs, you'll have a reliable, servicable system. So bring it on, let's see these systems are being done!
Cheers