rear sway bar?

I wouldn't worry too much about the effect of a sway bar on the unsprung weight of a solid rear axle. Once you add brakes tires and wheels you're looking at about 300lb for the whole assembly which is unsprung weight. Our rear bar weighs 7 lb and if you assume half of that weight is carried as unsprung weight by the axle, you're not changing the weight of the axle enough to be perceptible.