When I was looking through the early service information (1961) a few days ago, I noticed something very similar for unscrewing the cylinder, for some reason the socket is described as being 3/32" thick, which is clearly wrong (tool #11 in list).
The later manual mentions a different tool, which is very easy to make, I find a using a crescent wrench (adjustable spanner) is better than the flimsy bar (or ruining a screwdriver as mentioned in the manual) and the engine can be held in a vice using soft jaws (to prevent marking the crankcase).
David