1968 barracuda antisway bar

The Hellwig is hollow - so will be the lightest. Torsional resistance will be almost as high as the solid of the same dimensions.
Looking at the Addcos mounting - it is going to be a pain. Putting the bolts into the K-member hollow section you'll have to rely on threading the K itself - not good.
Firm Feel's sway bars mounting is well developed and tested as a bolt on product. That would be an alternative to Hellwig if you wanted one.