Hello Monica,
I am trying to picture the inside of the machine, it is very unlikely the screws were made to take an angled screwdriver because of the find adjustments sometimes needed, there is usually a hole or slot somewhere in line with the all the parts with screws, failing that to adjust parts inside the camstack usually has to come out unless it is part of the top shaft, if I have a search round and find a schematic of the machine I will have a look and let you know.
Ken
drivewithken@blueyonder.co.uk, September 2008