You're quite right Bartman, I not only didn't think about the fact there's two springs supporting the front end weight, but I didn't think about the leverage aspect of the spring's location.
Your comment about not compressing one inch of the spring confuses me though.
If a spring has a rate of 600 lbs/inch that means that you have to apply 600 lbs of force to the spring to compress the entire spring by 1". This rate is linear, so if the spring is sitting there with 600 lbs atop it and you apply another 600 lbs, it will further compress another inch. It really doesn't matter what the free length of the spring is.
One thing that frustrates me about Hotchkis is that getting tech info out of them is like pulling Rhinoceros teeth with tweezers. Apparently their tech people are unable to type words longer than one syllable. Every time I've written with very specific questions concerning their springs I get vague half-answers, as if the people writing the replies can't be bothered to fully explain what they're talking about.
Still, it's my understanding that the only difference between the big block and smallblock springs is the free height, the rates apparently are the same at 600 lbs/inch. They told me to get the smallblock springs for my '73 since I'd be moving the battery to the trunk, running aluminum intake and water pump, and making other weight-saving modifications.
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'72 Formula 400
12.77 @ 108 / 234/244 cam / Q-jet / 3840# / 3.23s / street tires (not DRs)
'73 Firebird 400/4-speed