Here are some pictures of the water pump with notations on bolt sizes. Note that the upper alt bracket bolt only attaches to the pump itself and can be fairly short. The lower alt bracket bolt is into the water jacket and must be sealed as with the corresponding bolt on the otherside. It doesn't hurt to put sealant on them all if you wish. I'd be prone to lean towards the long side on the bolts as there is room for them to enter the block without bottoming unless you really get carried away. All bolts are 3/8"X16 (3/8NC). The power steering bracket is a through bolt/nut only attached to the pump as with the upper alt bracket bolt.
I'd buy 3 ea 5", 1 ea 4", 1 ea 3", 1 ea 1&1/2" and 3 ea 1". You will also want a 3/8NC nut and washers for the bolts. I buy grade 8 for everything. Actually the bottom short bolts could probably be a bit longer than 1". I didn't have a spare front cover to check it with. Notice the location for the timing tab too. It uses those lower short bolts. This is with my '64 Dodge Polara. This water pump was the stock unit.
Rich Kinsley '64 Dodge Polara 4dr 318poly w/less goodies