I have bolted on the one head I removed. I am now ready to time the engine. The procedure in the book is not working. I have aligned the keyway and timing chain marks with the timing sprocket marks as described in the book. This isn't working because the book has you align the key way w/the LH bank of cylinders. Once you align the chain marks w/the timing marks on the sprockets, the cam is out of position. The drive pin is not aligned with the drive slot at the end of the cam. The slot and tab are supposed to be upppermost. The tab on the sprocket is, but the slot on the cam is down. When I try to rotate the cam to match up, a valve opens and strikes a cylinder and the cam will not rotate any further. I'm terrified I'll think I've lined it all up and crank the engine over and bend the valves. I've seen it happen. I've already potentially done enough damage to the engine with my previous mistakes. Please help me into the light at the end of the tunnel.