I use the same tool as Tim, but not quite so sophisticated, instead of a stick, I tension the tool to exactly the correct tension to align the top bolt by using the axle tommy bar (without the axle nut in place) to tension the tool, sometimes I add an additional tube onto the tommy bar, which affords greater mechanical advantage and accuracy, and before anyone suggests, I have been using this method for in excess of 58 years, and have not managed to wreck a fuel tank yet, but I suppose there is always a first time......