Help Identify This Old Spanish Coin From 1600s?

It is indeed the Spanish king, but those aren't the Spanish coat of arms - Spanish coins have lions and castles in the quarters. This coin has snakes-swallowing-children and eagles; this is the coat of arms of Milan, which was under Spanish rule until 1714.

Unfortunately, my 1600s and 1700s catalogues don't list Italian copper coins until 1750, so I don't have any references that list your coin. Modern editions of the catalogue do list them, and the NGC page for the quattrino if the early 1600s describes something like your coin. Google-image-searching for "Milan quattrino" came up with this example on icollector, which seems to more or less match your coin. Look below the bust (in the pic it's hidden by flash glare) for any remnant of a readable date there.