I got the flywheel lightened from San Jose BMW.
According to my household scale, the original flywheel weighs in at about 12 pounds. Maybe a shade more.

Stock flyhweel from a 1972 BMW R75/5 motorcycle

The new lightened flywheel now weighs about 8 pounds.
Taking off 4 pounds doesn’t seem like much but that is about 1/3 of the weight removed.
In addition to removing a few pounds and making the bike a bit lighter, this should allow the engine to work easier so the RPMs can climb and drop quicker.

Lightened flywheel from San Jose BMW for a R75/5 Motorcycle.