Where did the the crankshaft pulley come from? If it is original, it should be for a 5/8" belt. Are you certain that it is for a 5/8" belt? Your water pump looks to have a pulley for a 5/8" belt. If both of those pulleys are for a 5/8" belt, then you need to buy a 5/8' belt and change the pulley on the alternator to a 5/8" pulley.
Now if the crankshaft pulley isn't for a 5/8" belt, then you may have to buy a '53 water pump which comes with the narrower pulley. I don't know where you will find just the pulley. Even if you do, it is a bear to get the old one off and the new one on. The water pump costs $129.95 at classicparts.com. Who knows, maybe yours is about to lose a seal some time soon anyway. Easy fix.
Carl
