318 to 360

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The magnum head has 1.6 rockers which will lift the valve up higher than the standard heads that all have a 1.5 rocker ratio.

You'll simply needs springs to handle the new lift. When you order up your cam, tell them you have an older 360 and you did a Magnum head swap with a 1.6 ratio rather than the standard 1.5 ratio and you need a spring to cover the new lift. They'll hook you up.