Doug wrote an answer about Shimano Ultegra PD-6700 SL Carbon Pedals on September 25, 2012
I have a 1974 PX10 with Stronglight cranks. I bought new pedals after being assured that all pedal threads are the same. Well, they're not all the same. However, the pedal side on old French threads is bigger than the modern standard, so you can make a one-way transition to modern threads by having the crank side retapped. Worked for me. Most good bike shops should have the tap.