My understanding is most of the leaf's spring rate is in the portion behind the axle. The Hellwig product you posted helps with axle wrap more so than increasing spring rate.

Which front sway bar? Hotchkis 67-72 a body bar? With rubber bushings? How tight are the end links?

You should consider swapping to a ball joint style sway bar end link. Really helped with the lean on mine. Doesn't change your roll rates, just brings the sway bar in sooner.

I agree with upping your spring rates as well. Which you are doing. May just need to buy new leaf springs though.