It reverses every crank revolution too. Spark timing is controlled by the ECM, whcih calculates which coil pair to fire, and how much timing advance or retard is needed at the moment. The intake manifold shape changed every year after 1992. The early ones howled at 2100 RPM in drive, the later ones changed for size constraints in the car, and there was the switch to the Mass Air Flow system, whcih added another variant. All will bolt to the lower intake, but not all will accept the other various equipment needed.
Exhaust manifolds are pretty good for cast units.
I cant even imaging fitting headers to this beast, but you dont need to. I have run backpressure gauage on my car, and found no significant problem save the converter itself. Al converters are restricitive, but the exhaust is low on the list of places to get more zip from a 3.4. I cannot stress enought that this is NOT a car to give the kids going to college. The 3.4L takes frequent, extensive maintanence to assure its durability.