Cut the ACME rods using a hacksaw- make sure to clean up the ends of the threads where you cut the rod. Use some wood blocks or a cloth wrapped around the thread when holding the ACME rod in a vise for cutting so you don't damage the threads. File a flat spot onto the last 1/2" of the ACME rod- this is so you can mount the handles (or stepper motors) later.
Mount the slides by removing each of the end rail blocks. Slide the slides onto the rails and fit the ACME rod into the bushing in the opposite rail block. Slip the retaining collar over the ACME rod. Now slide the end rail block into place and secure it with the bolts that were removed.
Mount the 6" x 2 3/4" plywood motor base plate to the Z axis slide using 3/4" long bolts. Make sure it is square!