My welcome also, Frank on your first post. Your Ithaca does come within the accepted serial number frame for the Minier Model guns. If that's what you have then it had the shortest production run of all the Ithaca guns. Your gun should have only two pins and a smaller screw showing on the frame.
If you can access a copy of Mr. Walter C. Snyder's fine book on the history of the company, "The Ithaca Gun Company From The Beginning" you'll find a chapter on the Manier/Minier model beginning on page 50. Enjoy learning about your old double. Many posters here are much more learned than I to respond to your post, and I am sure you will hear more...Geo
PS: By the way there is a tutorial on posting pictures in the FAQ section.