#1,
Do not use all thread rod.

As far as cutting and threading the 4-40 rod, No, the rod is not full diameter, the threads are rolled on that rod which brings it up to size. If you cut a thread on the other end, it will be under sized.

You can solder a clevis on the cut end or get some 1/8 gas welding rod and make your own rods threaded on both ends. The welding rod is a bit thicker but with care you can thread it without any problem.

I also like ball links for a nice tight setup, but the heavy duty dubro horns have a long reach, which will allow the ball link to push off to one side, so it's a good idea to use the clevis' that come with them.