I've been collecting and studying the tool kit items for Healeys for a long time. I thought I had seen it all. However, just a few days ago I saw in the latest edition of "Roadster," the publication of the Healey Drivers Club, a photo of such a wrench. Now I have been to many autojumbles/swap meets, and I've dug through a lot of piles and boxes of old tools. I've been in contact with several of the biggest, longest-established used tool dealers in England off and on for many years, and I had never before heard of nor seen such a thing.
It would be quite a wild coincidence if the “AH100” casting meant something else, such as a manufacturer's code or model designation for the wrench, but it seems inconceivable that tools were specially made for the Austin-Healey 100. There simply would not have been any reason to do so. As I said, I've been a keen student of the tool kits for 20 years, and I've seen many original tools and tool kits, and never has anything like this come up before.
My official position on this is: I do not know. I'm very skeptical that the AH100 means Austin-Healey 100, but I can't deny the possibility either, despite how out-of-character it is for the time and place of the cars. I would not leap to the conclusion that it is definitely for the AH100, and if anyone else comes across anything like this, it would be interesting to know its origins.
Sorry that I can’t give you a definitive answer.