ideally, you would want to jack up the entire rear or the entire front for installation. once you have it installed and the bolt tightened, lower the vehicle and drive it on a ramp.. go back underneath, loosen the bolt and retighten to torque spec. It should be tightened with the suspension loaded.

40 lbs. is quite a bit. you might be able to get away with tightening it as tight as you can with a regular ratchet, but if the front is 72 ft. lbs., there's no way you'll reach it without an extended handle.