I have devised a design for a wooden frame/jig which enables one to
trim plastic keytops quickly with a modern router.  This produced good
results, especially when trimming 'Pyrolin' sheet replacements, in my
opinion the only way to go with antique instruments.  This is too complex
to put on any 'computer' medium at my disposal, so I will make up some
sketches this weekend and snail-mail them to you, and anyone else who
might be interested.  Please e-mail me your address.