Need to satisfy my curiosity, what are the threaded holes circled in the pic for? I'm guessing they hold a bracket. They're on my rear iron that's supposed to be from a '79.
I've looked all over various FSMs and parts catalogs. Looking at unmodified cars on Bring-A-Trailer didn't work because nobody takes photos of that area.
They show up in the catalogs from RX-2 to FB, though Mazda might have reused the drawings from the SA.

 

That is a drawing of an '81, since '79-80 did not have an oil pressure sender and '82-85 had a press in, not thread in, heater hose.

Except... what is that thing item 33 is sealing? I have never seen that boss drilled out on a carbureted car. GSL-SE and later have a PRESS in coolant barb there, for the throttle body heat.

Pretty sure that item 37 is what goes there.

 

I believe that's for the starter cables.

 

nuts, I thought I mentioned the pic is from the RX-3 catalog but that line must have been lost when I reworded my post.
For them the starter is on top and the battery is on the opposite side from SA-FB.

#37 is called out as just "clip", maybe for the wires leading to the coolant sensor and oil pressure?
At first I thought it was the crush washer for the oil cooler hose (seen it like that for power steering), but it's shown as 2 washers on another page.
Weird that both holes are threaded, maybe the thread tapper guy had a quota at the factory.

 

You made me look. I have those 2 threaded unused holes on my OEM keg thats never been removed or messed with except for some wiring and intake changes. I would say its for some special market purpose or for some special use of the engine. Maybe the factory used them in manufacture?