Can a fuel pump be rebuilt? or Spacer removed?

On my 77 Triumph Spitfire, I have purchased a replacement pump which will not install due to a difference in the curvature of the arm. Can the old one be rebuilt? The other option is where the old one used a spacer, could I remove the spacer and use the new one. I am not a mechanic, but I feel capable, yet I cannot chance doing more damage. I have photos of both new and old pumps side-by-side. Please help. Thanks!