Hi weeds, sorry for late reply but been having trouble with logging onto the forum.
Because i've got the old school isuzu motor I simply used a fuel selector valve/switch to select whichever tank. It has 6 ports so changes both the supply and return fuel lines over. This system can be used with any set up that doesn't have an in tank fuel pump, pretty sure tdi would be ok? Otherwise like you said a fuel transfer pump is the simplest option. I've priced a few but are open to suggestions on good value options out there.
For a gauge I decided to use a spare factory land rover gauge I already had, so I used a factory fuel sender. as most will be using a transfer system I've bought a vdo sender to test fit, and it will talk to a combination switch/gauge.
Cheers, Andrew.

