Rather than making the adjuster the way they have.

It would be easier to have the main tubes threaded left/right. Then have an outer tube that these screw into with lock nuts.
Basically making a turnbuckle that you can adjust in-situ

Or get the tubes of the correct ID so they can be tapped for L/R threads and use these in the middle.
It would be stronger and handier than having a threaded bit welded to the bush sleeve like in that kit above.
or just get the tubes and weld the threaded inserts into them as are pictured in your link above. No tapping required then

http://www.spohn.net/shop/Replacemen...-Adjuster.html