I recently purchased a 1980 10th Anniversary Black Gold car to restore.
The car is a decent example that runs and drives with the typical 280zx need for rocker panel/fender rust repair.

​​​​I would like to get a bit more street and track day performance out of it, but don't want to do anything irreversible to it as an all original car.

What can be done to add reasonable performance without hurting it as a collectible limited edition car?

 

Nothing. The engine is limited by the amount of air that can get thru the throttle body and intake manifold. The only way to get more out of this motor is spend 10,000.00 on a super rebuild and turbo setup or engine swap to a RB or LS.
The ECU is NOT tunable. This ECU is a one time flash chipset. You can get a mega squirt or or FAST fuel management system to be able to "tune" the fuel but those are about 1500.00 and you will still not be able to get more air into the engine. The Mega and FAST are more of a upgrade of the EFI computer, not a performance enhancer.
Your best bet is to get the engine running at 100% factory performance and enjoy it as it was designed.
Dont mess with the AFM as it will not get you more air to the engine, it will just mess up the Air/Fuel ratio.
FYI if you have an O2 sensor on the exhaust, it is a narrow band sensor. You may or may not have an O2 sensor. The O2 sensor has a very small part in the EFI fuel calculation. The CHTS (Cylinder Head Temp Sensor) is the most important sensor and then the AFM.

 

So basically it's either keep it all original, bare minimum pull the head and rebuild the top end completely so I could restore it back to original later, or pull the entire engine, store it, and LS swap it like my last N/A 280.

 

You can do a non-traditional turbo setup. If you go over to ZCar.com, Bonfire79 has a setup like that. He put a turbo on a N/A engine without all the factory Datsun 280zx turbo stuff (distributor, wire harness, ECU, knock sensor ect). Like I said, you are limited by the air side, a turbo fixes that. The L28 engines are super strong and can take a 500hp turbo setup. Blocks and cranks are really good in the Datsun. Nothing money cant fix. Now try finding a turbo intake and exhaust. They show up now and then but are not cheap. Not a lot of aftermarket intakes or turbo exhausts. You will have to look for stock stuff.