Step 2: Measure, measure, mark, and cut
Trim the 1x8 boards to 8' exactly.
From each of the 1x4 boards, cut (4) 35-3/4" pieces for a total of (8)
Cut the all-thread into (16) 9-3/8" segments.
Before cutting each section of all-thread, run the wingnut onto the rod. After cutting the rod,remove the wingnut over the cut end to "chase" (repair) the threads.
You should also double-check the length of your all-thread rods. I'd dummy one up and try it out before cutting all of them. It needs to be just long enough to catch a couple of threads and snug down without punching out through the cap nut. The actual "cap" portion of cap nuts is fairly thin, and if the all-thread is even a bit too long it will punch through the end when you snug it up.