For a street car an aluminum flywheel is a bit of overkill. The properly lightened stock unit can safely loose 5 pounds and all of it around the outer area where loss of weight affects centrifugal inertia the most.
The most productive change in the clutch assembly is going to a light alum. center no springs, clutch disk (see my website). the lack of wafer springs in the lining area releases cleanly and reduces wear on the syncros because residual drag is absent(that caused by the lining expanding on stock springs)and the light disk reduces the force that the syncros have to speed up or slow down with EVERY shift.
As for lightened gears it is OK if you are talking racing applications. But so little is lost in weight it is hardly worth the $$ except for the concept and personal satisfaction(and bragging rights). I`ve done them for years, but the real gain is from the replaced syncros & sliders and repaired or replaced shift forks. If you have to do it stick to the large gears, and for goodness sake don`t cut down the layshaft as pictured in Msiert`s pic below. All that cutting only reduced a few oz. of weight, at a point of no reduction on centrifugal force, and significantly reduced the shafts regidity, as the surface hardening is only about .040 deep. Yes the shaft can handle twist forces ok, but pop the clutch out in 2nd gear (as in serious downshifting) and suddenly your layshaft is a bit

eccentric. Don`t bother to ask how I know..............
Loosing the heavy stock disk results in the best shift improvement.
By the way, nothing is similar or interchangable between a Alfa transmission and transaxle other than syncronizer pieces (from late 115 to 116/119).
Pic is of alum centered disk that can be used in 105/115 and with center spline change in Alfetta/Milano. The 4 puc is only for racing where higher torque clamp force is wanted (generally not needed in 4 cyl cars0
Other pics of lightened parts ( ring gear) and internals of my GTA box while getting syncros & dog teeth assembly replacements.