Depending on how brave you are, you can idle the engine with the valve cover off and you'll get a really quick notion of where the clacking is. Depending on what kind of rockers you have, it can be really easy to use a ratchet with extension and just loosen and tighten a half turn at a time to see where the noise is too. Can't do that without the engine running! The only issue is that you *might* get some motor oil everywhere.
Here's an example with an SBC where the guy is using a piece of cardboard to keep oil from running off the rockers out of the engine.
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Doesn't sound like you do this sort of thing much, so maybe don't try it.