I might be being too logical here, but since they are Isky springs and you have a Part# on the box, you could call Isky Cams and ask if they have a record of the old part#. They might be able to provide the specs.
No guarantee the springs match the box unless the Part# is stamped into the spring. I would just have someone check the pressures at a given installed height and max lift to be sure. Diameter (for application) can be cross referenced to currently available springs.
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Triple Black 1971 GTO
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