Injection cars have two 8mm fuel pipes, flow and return, as the whole system is pressurised. Use modern plastic pipe.There is a 14mm flexi feed pipe from tank to pump.
But, if I was you I would be putting in a late Vectra A tank with internal pump. Much simpler pipework and should be easier to find but must be a 2.0 pump not 1.8. Needs an access hole in the floorpan under the rear seat (round plastic cover needed too) and a pump electrical connector there.
If you are going to use E10 petrol seal the inside of the tank before it goes in and use E10 safe pipework (no steel).
Another reason for the Vectra tank is the petrol gauge sender. Mk2 injection versions are hens teeth selling, if you can get one, for £150+ or 180 Euro out of Germany.