I have a s/a A10 1961 and have no adjustment on the gearbox lug. There is, however, adjustment on the actuating lever just inside the gearbox cover. What I do is slacken off the clutch on the bars about 2/3, then adjust on the gearbox lever quite tightly, then finely adjust on the bars.
Fixed kickstarter is a bit of a PITA at times, but it works so I live with it.