You might really want to look into cryogenic treatment on the springs. I have at minimum my springs and rocker arms treated on all my engines. The harder the intended use the more components I have treated. On my 499" engine I even had the Victor intake treated to relieve the casting stress since I knew it was going to get heavily ported and I didn't want it cracking later.
In the link below you can see a short video from Circle City Cryogenics that has my K-Motion valve springs, a USPS box with my rocker arms hanging out, and my Victor intake getting the -300 degree treatment.
The process makes the valve springs last without loosing pressure over time.
Tom
