Or maybe some kind of guard for the blower motor?  The contour of the bottom looks similar but without knowing the distance from the bolt holes I'm just guessing. 

Where's Waldo type a thing.

1 hour ago, zKars said:

Me thinks this is a speaker guard.  Why a speaker may need a guard is another question...

I've got one of these laying around...it was a guard for the driver-side only speaker.

 I agree the "unknown plastic piece" is a speaker guard. They were used to protect speakers from dripping water damage when the speakers were installed in the door panel, or almost anywhere in an old Z.

Niles Manufacturing provided automotive switches to Nissan.  I don't recognize the piece.  Perhaps if I knew where it came from on the car.

Hitachi voltage regulator for the original "grapefruit style" alternator.  Covered in undercoating.  40amp (45 amp?) capacity TL1Z-37

Oil pressure gauge sending unit.  The original sending units had a bayonet plug fitting.  This one is either aftermarket or later model type with the electrical fitting changed.

Speaker cover (as required to deliver the proper base vibe.  Commonly known in speaker techno circles as the back-plate acoustic reverberator bouncer designed for single speaker AM audio systems.)

 

30 minutes ago, 26th-Z said:

 

Speaker cover (as required to deliver the proper base vibe.  Commonly known in speaker techno circles as the back-plate acoustic reverberator bouncer designed for single speaker AM audio systems.)

 

 Thanks for that info. I didn't realize the covers affected the acoustics.

Crusty Rusty Bracket Anyone?

Another Bracket? Seems familiar like for a jack?

Unknown seal...

Unknown plate... could be just junk

Vent Clip of some sort

3 rubber elbows,,,, I'm thinking quarter windows?

Strange rubber plug... no through-holes.  Could be junk in the pile of parts.