Thanks Folks-
The upcoming job will be 70-30. It strikes me so odd that welding ERCuNi on A-36 permits a welder to qualify on Cu-Ni, but since it is permitted in QW-423, I will take advantage. I certainly understand there is a skill level that may get overlooked when substituting materials on a performance test and would usually opt for the actual production condition when possible, but in this case we will be qualifying one of our very best so I really have no concerns.
Thank you all you have helped tremendously.