From my own personal experience with 440 heads, the header bolts require sealant, like ultra-blue, on the threads or they will leak coolant. 440 heads exhaust manifold bolts do go into the water jackets, so sealant is required. Could the water coming out of the exhaust be condensation? Do you have sealant on the header bolts? Those are 2 questions that may help diagnose your troubles. Good luck!