That serial number would make your gun a Flues model from 1911. It very likely started life chambered for 2 1/2 inch 20-gauge shells. In those days Ithaca was making many of their smallbores very light and many of the thin sidewalls of their frames have cracked from years of North American Nimrods serving them a steady diet of all manner of Super-X type 20-gauge shells.
A little more explination of 'crazy single trigger" please? Ithacas of that age are quite often found with the Infallible Single Trigger made by Lancaster Arms Co. They have the selector along the left side of the top tang.
