As someone who has lost his AR keys several times, broken a few off in locks & had his 75 ignition lock fall apart outside Hughs' workshop, here is the easiest way that I have found for 75's ....& their derivatives. 30 minutes the first time, 15 minutes from then on.
The lock screw is tight, but not rediculously tight as the head break off torque is quite low. Remove the upper & lower shrouds, the top one slides out if you lower the wheel down. I use the corner of a small (10mm wide) cold chisel & 8oz ball pein hammer to cut an angular slot into the outer edge of the lock screw. The direction of attack is from the drivers side, behind the wheel & inward, ie the way it will undo. Once you have a decent mark, but not too much as it will lock the screw even more if you spread the head, then change to a small pin punch, or similar. Lodge it in the outer part of the slot & with a couple of good hits from a 16oz ball pein it's undone. Replace the screw with a socket head screw, 6mm D X 1.5mm pitch from memory & not longer than the original, else it will jam the lock. A slotted head screw is OK, but the socket head is easier to undo next time round. Use a lock washer under the head, or screwlock Loctite.
105s are similar except you take off the shroud, then the switches & access the screw heads from the side.
The same process applies for the classic Range Rovers, except the screw head is slightly proud & you can slot it with a mini hacksaw blade. No Range Rover owner jokes, thank you.
Have fun, Kim