A late 80's/early 90's camaro with dual fans will have the secondary fan switch (on at 240*IIRC) while the primary side on those cars was handled by the ECM. I'd look at the Grand National applications and see what their on/off temp is.
Your Napa should have an "Echlin" catalog with all of their electrical fan switches in it. They tell you how they are wired, thread pitch, and on/off temps. Ask them to let you look at it, find one that you like the temps of, and go with it.