Stuart is right. If the lobe is in the wrong position it can be a bear to get the bolts in. Another thing to check is he may be trying to put a later model chevy 6 fuel pump on & the fuel lines don't match up.
I had to replace the pump on my 38. I went to the local parts jobber I normally use to see if they had one. Their book didn't go back to 38. He brought out the earliest chevy 6 fuel pump he had. It would bolt up but the fuel lines were positioned different. Instead of running parallel to the block they ran on an angle. I took the top off of the new pump turned it so the fuel lines ran parallel to the block and it fit the old pump bottom perfectly. My fuel pump is now a hybrid with a "new" top & original bottom.

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