I'm looking at purchasing a NOS fuel pump. What would you experts think regarding the diaphragm and other internal parts as needing to be replaced?

Yes, yes, yes.

My personal experience is that any fuel pump that is older than 1980-ish suffers from a fairly quick failure rate.

The failure? THE RUBBER DIAPHRAGM. It turns to goo within a week or so.

The reason? THE NEWER GASOLINE ADDITIVES - IN PARTICULAR ETHANOL.

So, my suggestion is to buy the pump, but DEFINITELY replace the diaphragm with a new rebuild kit that contains the newer rubber.

Youngfalcon
As Bill suggested replace any rubber part before fitting or you will do the job again in a short period of time.

It does ruin the "NOS" part of the deal but I would consider that a very unimportant point.

Tony