This particular IH is not a fatty, it is a bronze Longacre. There were three types of IH's in 1864, the first ones were "fatty's" or Copper Nickel, they were thicker than the bronze varieties. The second is the one I found, bronze but not a Longacre. The third and most valuable is the one B Spa found, a bronze Longacre. If you look at all IH's minted after 1864, they have a very small L on the ribbon below the headdress, like B Spa has pictured. Here is the one I found, also in very good condition, the 1863 Copper Nickel IH, that I found 6 inches away was in terrible shape. The nickel doesn't seem to fair as well under ground.
[attachment 333374 1864IHBustsmallerfile.jpg]
[attachment 333374 1864IHBustsmallerfile.jpg]