heads for a 318

I have a set of Magnum heads I've been thinking about running, but I'm still not sure about one thing: Valve Springs.

I have a Comp XE268H which is going to be in the .515 lift arena with the Magnum rockers. I doubt the stock springs are up to that.

The Mopar option is machining to accept the non-beehive springs for LA heads with some very spendy retainers from Mopar. I really like the beehive springs and want to keep them.

Is there a low cost alternative for better valve springs for Magnum conversions?