According to Rockauto, they use the same front springs, MOOG 6452.
That's the same thing I found under Moog......
6452 for G10 and G20
6454 for G20 and G30
6560 for G30 only
You may already have the larger/heavier springs from the factory. Check your wire diameter on the existing springs. If it's about 0.82" then you have the heavy springs and the 6452 will be softer. The 6452 wire diameter is about 0.78". The GM G10 springs (softest) are 0.75" if you can find 'em in a junk yard.
There's no difference in the free height between 6452 and 6454 just the wire size.
The 6452 is rated at 3155 pounds while the larger wire diameter of the 6454 is rated at 3840 pounds.
Specs on every coil Moog sells: http://www.moog-suspension-parts.com/universal_coil_springs.asp