I'd have a look in this thread first.
Here I did this when assembling the pump above ^^^ and it went together a treat.
One thing to watch out for on that era ('60-'64?) pump is that there is one single bolt holding on the very top plate. This has a very fine thread and due to soft nature of the metal used in the pump itself, the threads often tear loose giving leaks.
This is what the one above was like before I rebuilt it. I found the original bolt to be around 20mm long (this was many months ago...:?: ) but the threaded hole in the pump could accept a bolt about twice as long. I found a matching thread bolt, even the head looked identical. After tapping a new thread into the pump, it went together as good as new, and no one will ever know.
Just a tip, and make sure you dont cross thread it putting it back in. :wink: