www.speedwaymotors.com sells left hand taps in US sizes. They also sell high quality heim ends and threaded aluminum and steel tubes to make the links with. They have clevis type ends also. I have thought about building my own also.
After much thought I have decided that solid bolt in rods with out the clevis ends like the Kafer Cup braces or heim ends would be more rigid and cheaper. As Martin said, with the chassis available, adjustability is not necessary. I think with the engine in place and on the ground so the chassis is where it would normally be before the flex of hard driving is applied is the place to build it to.
ken