Need new gas tank + whole system. Advice?

My observations from looking at the pics..

The tank is done, should be replaced. Spectra makes a factory original. Available at Nappa Auto parts.
Filler tube could probably be reused but you need to remove it and look at the portion that goes into the tank to see if it is rusted. Vans Auto carries new tubes. Also, the filler tube grommet at the end should be replaced. New sending units are available. Bouchillon Engineering sells a stainless steel version , I have one myself, works perfectly with the factory gauge and the sealing ring on the sending unit works fine. I've been using mine for 3 years with no problems.
You have a piece of rubber line in the gas line at the sending unit where you installed the electric fuel pump. That took away the ground path that the gas gauge needed to work properly. Quick test.. connect a jumper wire to the tank and the frame of the car. If the gas gauge starts working, that's where the problem is.

Hopefully others on here will add their observations as well.

BTW, how did your car get to Germany??

Nice Cuda!!

Cheers!!