TAKID455 is right. The stock compression on the 403 is a dismal 8:1. Swapping to the earlier heads will bring it up to 9:1 and will make the RPM cam work.(be sure to use the valve springs too) You will find it to be really sluggish with the stock heads. The Edelbrock heads have the larger big block ports but also the larger combustion chambers which puts you right back around 8:1 or less. This would be a very disappointing swap without some flat top pistons. The Comp Cams roller tipped rocker arms are crap. Spend the extra bucks and buy the full roller rockers from Mondello. They bolt right on and work nice. Either the RPM intake or the Holley Street Dominator intake work well with the combo. Motor will pull past 6500rpm with no problems. Unlike the junk cast rods that Pontiac gave us the 403 rods are virtually bulletproof. Now after spending your good money making some horsepower, don't forget to put a decent gear ratio in the rear end or it will still be a slug. Good luck
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