I have a 1976 280z.  Bought it as a shell and I am redoing everything.  Under the dash, in the upper kick panel area on both sides it appears there are round openings that have been tack welded or riveted and sealed shut.  

I also have openings to passageways in both inner fenders up by the core support.  I ran some fish tape down the passageways and I'm wondering if they connect to these openings that are blocked off.  It seemed like they would connect.   I would love to potentially use these to run wires through for a cleaner look.  

Can anyone shed some light on this?  Maybe these were fresh air intakes?  If so, how were they controlled?   Are the block off plates factory or added by a previous owner?  If I open them up, will I get a large amount of air coming in while driving at speed?

Thanks

I think you might have a post Aug 1976 build ie a 1977 car. Those side vents are open on a 75-76 car with plastic inserts in the round plate area. These would be controlled with the knob/cable in you other post. There would also be a pleated plastic elbow in the front hole for a scoop type inlet. They must have changed the fresh air intake on the 77-78. I have a shell I can confirm this idea. 

The hinge plates look like the later 77-78 style. If you have a picture of the door jam latch that would confirm the later build date. Better yet the drivers door jam plate with the build month/year. 

Well then I find my 78 car has open holes under the dash. Then has no openings up by the core support, just a small hole. Odd. 

Car is titled as a 1976 and the build date on the door jamb tag is June 1976.

Wondering how these block off plates are attached.  It looks like the factory plastic vents are attached with small bolts?  The block off plates definitely don't have bolts or screws holding them on.

They look like they are spot welded.