To speed along installation of a CoRE labs OTS, hang one long rail perpendicular to the rear wall, tighten securely.  Hang the second long rail, with the Unistrut bolts slightly loose.  Take a piece of the wooden packaging material, cut to 48.125” in length, then use this 48.125” piece as a measuring jig, inside to inside of the longitudinal rails while tightening the second hung rail.  This should allow a pair of installers to hang the long rails in only 30 or so minutes with perfect alignment...