My vote is for a 6-point socket (the corners of the head are deliberately rounded, making a 12 point apt to slip), and an air impact wrench. Works a treat, every time.
2nd choice is the same socket, with a breaker bar and a length of pipe for a cheater. If everything is installed and in good shape, you can maybe lock the engine by putting gearbox in 4th and setting the hand brake firmly; or use the rope trick.
If those don't work out, position the breaker bar near (or on) the frame rail on the LH side and hit the starter.