Don’t even know  what to call the part , but it’s cracked and don’t know how important it is . Can I used an earlier metal bushing ?

I am pretty sure that the metal one will swap right over.  I remember messing around with a bunch of parts and realizing that Nissan had done some cost-cutting.

Looks like it's called a set collar.  It just sets and spins.

http://www.carpartsmanual.com/datsun/Z-1969-1978/electrical/distributor/280z/12

Yes, you should have no problems. If you bought a rebuilt cardone distributor it comes with a metal collar. I rebuilt two old ZX distributors last summer and one had a plastic collar and the other a metal one. They both fit fine.


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That part affects is the axial end play of the distributor shaft in the housing. If you switch over to a different piece (whether that is plastic or metal), you should check the end play and adjust the gap filling washers accordingly if necessary.