I specced the M suspension on my Z when I bought back in 04 and when the inevitable happened I replaced all the springs with Eibachs to prevent it from happening again.
However to answer your question I have just had a look at several aftermarket solutions and they all quote they same springs for all the 6 cylinder engines of that time, the 4 cylinder 2.0 being the exception.
With that in mind I would stick my neck out and say they are the same, for some reason I can't the spring table on my ETK catalogue to work and RealOEM doesn't seem to have it.
