Yep a Torque Multiplier is Number 1, you can put 500ft/lbs on with an 1/2inch drive(just don't use your inch rattle gun on it),and a couple or 3 leathermen on your belt,especially the "Crunch" which has its own mini vice grip,great for undoing stubborn Phillips head screws.
You don't need a torque wrench on the sump plug,just belt the spanner a couple of times with a copper hammer(don't want to hurt the spanner),and if it leaks plug it with Quick Metal epoxy,easy.