Looking at your photo and the diagrams I posted I would say it is a HJR type gearbox.
Are the parts you need information about numbered 38, 39 and 40 in the diagram? If so they are the operator plunger. To set plunger it should be screwed home and then unscrewed half a turn to ensure plunger engages in V slots in the operator (part 47) correctly. Screwdriver slot lies in the same plain as head of plunger.