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I'm sure you can find lots of old threads on the Ford parts system. Briefly, the '5' in 59 indicates the year that the part number was released for production. In this case, 1945. The '9' indicates that it was a Mercury part number. So, your block could be from 45 through end-of-production. The 59 blocks are generally considered to be 46-48, although we know there are exceptions. And, just to be clear, both Ford and Mercury used the 59 block, 46-48.
Edit... 59 blocks generally came as 3-3/16 bore (3.1875). A few came with a 3-1/16 bore, and per info you will find in old threads, the 3-1/16 bore blocks are thought to be 'replacement' blocks, bought at the dealer parts counter, intended for replacement in pre-war vehicles. So, probably, speculating here, your block could have had a .030 re-bore, with some wear out to 3.22. Or, maybe standard bore with LOTS of wear. Look at the tops of the pistons for a stamp, like 'std', or '.030'