Did you remember to install the 1/8" pipe plugs that live behind the sidecover? There is one in the middle and one in the lower rear corner (usually).
Do you recall, when looking at the block deck, if the passageway thats next to the head bolt was plugged or was it open?
Some 58-62 blocks had this plugged in conjunction with a special drilled head bolt. This was done when these blocks were retrofitted to the top ends from 53-57 engines. If this was done, there should be a special drilled head bolt present that can be identified by a "O" on the top of the bolt head.
Did you pour any oil into the pump before installing it?
Try pulling the pipe plug on the side of the head and priming the pump as Drew suggested. Sometimes it can take awhile longer than expected...
