Go to your local hobby shop and get some brass shim material in various thicknesses - in the range of 0.0015 through .0040 (1-1/2 thoudsandths through 4 thousandthes). Cut a piece that will fit around the shim. if the gun goes together and the hook is not too far to the right and the gun is tight you have it right. If it is still loose go to a thicker piece. If the gun won't go together then put in a thinner piece. Just leave the brass on the pin. Go out and shoot the gun and see if both firing pins do the job.
I haven't tried it but the feeler gauges they sell in the automotive shop look like they would make good shim material too. Use at your own risk. I have done the brass shim bit with good results.
Best,
Mike
