308 heads are not an improvement in compression, they are open chamber 360 heads, 302's are closed chambered.

308 heads http://www.forabodiesonly.com/mopar/showthread.php?t=60004

302 heads http://www.americancylinderheads.com/cyl...s-_-AC108C.html

308 heads are swirl port, medium sized valve heads, 302's are swirl port small valve heads.

Don't spend the money on either, magnums are better than both.

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They say there is always the exception that proves the rule.
Don't be the exception.