Looks like my rough idle and lack of high end power is now traceable to a burnt valve and lack of any compression on my number 7 cylinder. Have been researching replacement heads in case that is the route I need to go. Engine has not been dismantled yet. Been finding some conflicting info on the heads for this engine. The Volvo Penta Store has the VP #3856929. When I look this up it appears to cross to a casting number of 14102193. I assume that is the GM uses to identify the head. These heads are readily available and relatively cheap as remanufactured items. Following this on several engine boards though it appears that there is some debate over whether this is or is not a vortec head. Anyone know?