All-thread is not your friend and should not be used in this application just to save a couple of bucks. A solid tie-bar with threaded ends is the correct way of doing it and they can be had for $26.95 with all the hardware from Motovation. If you're going to do something, then do it right.
Keep in mind that trying to do it cheap will probably cost you WAY more money if you ever go down. Low grade all-thread is to soft and grade 8 will more than likely snap off. Solid tie-bars are by far your best bet. See my above post.
I visit three forums, based upon my bikes. On every one of them someone is trying this. If you are doing it for fun and experience, great. If you are doing it to save money, not great. Because, as noted above, it will cost you a lot more if you dump your bike (which several folks have proven).