Yes.
You'd do all of those, plus go with aftermarket EFI, plus put lots of very trick coatings on the engine internals, plus you'd go through the oil system and everywhere in the engine that air has to move and help optimize that flow...
A good high-quality exhaust would be mandatory.
If you didn't want the engine to last very long, you could monkey with the cooling system so it didn't pump as much air. (It takes power to pump air; that's power that doesn't go for moving the car.)
Notice that most of those are the same things you do when trying to make the most powerful engine possible? Because they are increasing efficiency. The thing is, for max MPG you have to increase the engine's efficiency
while it is at cruise RPMs and throttle openings. Which are "kinda midrange" and "very small", respectively. Most "power" setups are optimized for WOT and high RPM.
Note that you can gain significant fuel economy by keeping your tires inflated to spec (or over!), keeping the engine in good working order, and by using a very light foot when driving. Not that the latter is any fun in a 914....
--DD