I am in the initial phases of a Pocher Mercedes…I have researched this problem with the screws and have the following info. It is advisable to run a thread cutting tap through the hole prior to screwing in the screw. Apparently the thread size is a unique thread from England used back in the 1950’s, 60’s. The thread size is a 1/16 British Whitworth Thread (BSW thread.)
While they may be difficult to find I did find a supplier in England who sells watch repair tools. (Google is a great thing) It was not expensive. This was a while back. I forget the name but if you google 1/16” BSW Tap you may find something.
Otherwise I was told to heat the screw prior to screwing it in but the screws are so tiny I think it would be difficult