Small block water pump pulley question

Ok, I’ve got a 1970 dart I’ve been working on forever. Originally a slanty, putting 340, four speed into it. Motor is in place with the rest of drive train and the pulley I have for the water pump isn’t deep enough to line up with the alternator. There is only one belt, manual steering. Is there someone here who can educate me regarding what it should be.? Frustrating as I am close and would hope to get n the road before it gets cold. Thanks in advance for any information you can provide.