There are 3 excellent books I would recommend. The Ultimate Guide to Attributing Bust Half Dollars by Peterson United States Early Half Dollar Die Varieties by Overton & Parsley Bust Half Fever by Souders You may also want to check out the link in Bonedigger's signature line..... Alan Stullenbarger
Boy, they really used the dies up back then. Look at "America", the letters are really flowing towards the collar, which I assume was cracked?