[Stan]

I would be very careful about leaning out an L-24 engine. They were prone to lean detonation in their day, and are more so with modern unleaded gasoline. I would not do this without having a properly functioning stand-alone A/F meter installed (or at least a quick reacting EGT).

OTOH, while air injection systems do all those things you mention, in combination with a modern generic cat they also dramatically clean up your car's HC emissions. The car will produce slightly more CO2 than it does now, but compensates by dropping its HC emission to near-zero. I helped a friend do this to a similar vintage Toyota that was getting busted for HC emissions, and a generic Chevy 350 cat with the right in/out tube sizes dropped HCs to nearly nothing.

Long-tube 4-2-1 headers uncork the exhaust side of the L-24 very nicely and bring a nice little bump in performance/FE. If you buy an unpainted set, you can have any muffler shop weld in an air injector bung and an A/F or EGT bung, then have the whole thing ceramic coated. A header like that will save considerable weight over the OEM cast iron manifold, improve FE and last the life of the car.

For better FE I also recommend looking at swapping to one of the taller diffs that came in later Z-cars (like the 280Z 2+2). Check out the many websites dedicated to those cars for details.

It's all good!

Stan