LS1 valve springs in a early model block?

So i'm looking at some valve springs on ebay that are listed as LS1 valve springs. Comp Cams 918's (2481540642). Now the specs on them say that the
installed height is 1.8" which is different from the stock ones that fit my heads but the outer diameter is the same. What (if any other than installed height) is the difference between these springs and other springs. I'm looking for a stiffer valve spring and am looking into any money saving options that might fit my application. Thanks in advance.
-Bruce 89 305 TPI
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