Well they found mauls of very different sizes at Stonehenge.

The thing about the Ford engine hanging from an A frame, you could make it fairly accurate by having the sarsen laid flat in front of it, and aiming it, and maybe having timber guide rails for the string, then moving the sarsen along a bit when you'd done, and repeating the process so the result was consistent. Spookily, Henry Ford re-discovered this technique and changed the world.

I seem to remember we designed another version, do you remember? A maul on a rope with the sarsen directly under the A frame. Then you'd have two teams swinging the maul to each other and, depending on the exact length you made the rope it would take off an exact amount of the stone surface - and you'd know when it had done so as the maul would no longer scrape the sarsen. It would be an easy way to produce the slight bowing on some of the uprights and the curve of the lintels.