The screws in Japanese cameras are typically all normal metric screws. I suspect that these are M1.0 size. Ideally take a small metric screw of the right size, point the end with a file, cut off the head, and cut a slot with a slitting file or jeweler's saw. Not hard with a modicum of hand tools.
Taking off the shutter speed dial is tricky. Two screws are short, one is long. I think you only loosen all three. The short ones are only accessible at one ASA setting each, loosen them very little. They can't be out too far, or you won't be able to change the ASA setting, which you have to do. The long one is always accessible, it can come out a bit more. The long one is always through the slot in the ASA dial/gear, and keeps that dial from rotating more than 180 degrees relative to the shutter speed knob.
I know that DAG had at least one of the long screws, since my 7s came with a short one there, due to muddling by some previous repair person. He replaced it when adjusting the focusing and meter on my 7s.