Without a doubt, the challenge is getting the splines to line up and mesh home just right so you can stab the gearbox all the way in. I've found that rotating it back and forth and rocking the back of the gearbox in a circular motion makes it the easiest to line it up and slide it home, however, I think the long threaded rod is a great idea! get the weight of the gearbox off your hands/jack, and give you the freedom to wiggle it around while getting the splines to line up