Made the screwdriver slot but I don't have a screwdriver with a wide enough tip, so I'm going to have to wait until tomorrow to get my hands on one probably.

As for the last question, it was a park tool crank puller. But I don't think it was the thinness that was the problem, after all a ratchet fits in there to get the bolt out. But I've never had any other crank puller so I can't compare.