4 reales Spanish Carolus 1788. http://www.ngccoin.com/poplookup/world-coin-prices.aspx?category=8038&worldcoinid=28594
From what i can tell i would say original ,though in this condition you will not get much of a premium over melt because it has 2 holes and its worn to hell, also their were die variations that will explain your marks !! if you got like 20 bucks that would be a lot for it !!
my bad its Mexico. Here it is: http://www.ngccoin.com/poplookup/world-coin-prices.aspx?category=13646&worldcoinid=46078
Have you weighed it? If genuine, it's pretty worn, and tbe holes are the coup de grace insofar as its condition goes. Sometimes holes are made so that a coin can be worn, and other times they constitute a cancellation to indicate the coin is a counterfeit.
13.5g is where it should've been when new. Wear and the holes may well account for the variance. Supposing it's real, its condition issues make for a coin that will command only a very slight premium over its bullion value.