The most important thing about putting the new heads back on is to torque them to the correct torque, and tighten them in the specified order. First just snug them all, then use three different tightening sequences. First about 1/3 of the overall end result, then 2/3 then finish. And make damn sure your gasket is on right. Then with the intake manifold, use Blue RTV in the corners instead of the gasket. Tighten those bolts using the recommended lbs and use the recommended sequence as well. I believe that information is in the FAQ at the beginning of the Classic section.