The absolute best advice given so far is stick with the Simplex rear derailleur. Believe it or not, they do work very well. The worst kind of advice is altering the frame of a highly desirable vintage road bike by hacking, drilling or filing. Why ruin something that is becoming increasingly valuable and hard to find? Just my opinion but if my opinion saves just one frame from the hacksaw, then I will feel that I have done us all a favor