Good morning, JOB
Some of those pump castings were cast iron and some were cast aluminum. The cast aluminum bodies are very easily damaged.
There are some special fixtures that aid in the dis-assembly and re-assembly of the pump.
If your dealer has these fixtures and knows how to use them, you would be wise to let them rebuild your pump. Should be about an hours labor charge.
As you already mentioned, these pumps are no longer available. You can't afford to ruin it.