[s-cars] Fuel tank replacement

[Radek]

Hello;
We are replacing the fuel tank on 1996 S-car, due to rust.  Took out the old tank and removed the fuel pump.  Looking now inside the new tank, which has been bought "refurbished", we can see that the fuel pump will not fit.  There is a large plastic contraption inside, with three studs sticking up and three clips on the outside of each stud.  It's a totally different arrangement than on the S-car.  I suppose the replacement tank comes from a different version of Typ 44 car.  What are our options?
- try to return the replacement tank and be left with a rusted tank (can fuel tanks be welded?)
- try to fit a fuel pump that will work in the new tank (what about flow rate, connectors, etc.)?
- ???
Will appreciate any suggestions.  Thanks.

Radek & son.