Some will ask why so I will answer that now..
How many have checked new stock springs? Well I have, they are border line wrong for a stock motor much less more fuel and more boost..
Some of the valve prints on pistons are strike's during valve float. With a low pressure spring and added boost psi, miles & years of heat cycles the weak stock springs just don't cut it.
So for under 100$ new custom specific springs is always a good bang for the buck.. Everything in the valve train is weighed, cam specs, boost & back pressure, rpm, etc are taken into account and out comes a spring that will best suit a build.
After all we know GM didn't spare anything during production on these motors don't we...