Lightened flywheels get the rpms up quicker but you lose that low end torque curve a bit. i think it works out to quicker to speed but not very long legs. good for the short track not so good for long hauls.
The heavier the rotating assembly the greater inertia and momentum stored. This sounds stupid but if you think of what your trying to accomplish this might be a plus or minus! Lighter wheels will turn easier (greater rpm) heavier wheels will be harder to stop (torque) Multiply the difference in weight then think in your head how hard that differential would be to stop if it were turning 800 rpm. Flatheads build torque through the nature of the beast. Rice grinders build rpm.
That IS a lot lighter! (At first I assumed that they were just drilled, and would suggest "stuffing" them.) The questions become: Are you going to carry a passenger? Push a windshield? Gear high for modern highways? Run stock cams? Then wheel weight is preferable. If you want to race from stop light to stoplight, or actually compete in vintage events, then the light wheels rule...Cotten