Flywheel question

I was wondering this morning (as I was dreaming about spending money I don't have):

Do all engines have flywheels or just ones w/ manual transmissions? Would it screw lots of stuff up if you were to put a lighter flywheel on an auto tranny?

BTW, the budget of money I don't have is as follows on my 350Z:

Hotchkis anti-roll bars (adjustable, hollow) $400

18x9.5 identical wheels all around (plus spacers for rear -- allows tire rotations) + tires (undetermined) ($900 to $1200)+$800 roughly $2000

Quaife limited slip (that's torque biasing, not clutch, correct?) ???

I'm guessing that the above would get me to around 1G on street tires based on an article from SCC.

After that, I'll probably be 10 years older... : (

Automatics typically have flexplates, which are merely thin plates of steel or aluminum that the torque converter bolts to. The flexplates can't get much lighter nor do they effect things as much as the clutch/pressure plate/flywheel does on a manual-equipped car.

On newer cars, they are starting to use flexplates with a friction plate bolted to the face along with the clutch/pressure plate.

The torque convertor acts as the flywheel.

I figured that might be the case...