To answer your question........ the small hole to the right of the dowel pin hole in your first pic is a coolant hole.

If the leak is as minor as you say, I can’t imagine that a dose of stop leak wouldn’t solve it.

As for the composition gasket......... mill the heads .020 and use a Fel-Pro 8519 gasket, and you won’t lose any compression...... as well as have a flatter head with a better surface finish(if done on good equipment).