got lazy so bought a tr7 alloy fuel tank from Ian Wilson's Triumph Rover Spares in Adelaide. Folowing are some pics of the unit. It has an inserted fuel pump that can support RV8 FI:
I have not measured capacity but believe it to be in the 45 ~ 50 L range.
The cost is is more than i would have liked to pay, > AU$1k. but given the impedance of provision of the solution against my time to design and create a bespoke solution it was worth the expense.