I have built a mess of them there magnums and never come across any upgrade spring using the stock retainers. The closest thing I have found for a cheap simple upgrade is the GM 3100 springs and retainers, they give just a little more pressure with a little lighter retainer for a nice overall upgrade that will work with mild cam upgrades. I have also shimmed the stock springs for very mild upgrades or just when I want to turn a stock cam higher RPM because I got rid of the beer barrel intake for something more performance oriented, they tend to be happy turning another 500 RPM with any better intake.