Big Block ticking? Flat tappet cam. Normal?

You can hear it clear as day not firing on all 8 cylinders. I wouldn't start it up until you check what the problem is . Take the valve covers off and the spark plugs out. Make sure you have no tight or loose rockers. Then do a compression check on all cylinders.

header leaks at the head can sound like a lifter tap. But a dead cylinder and a tap I would question.