Originally Posted by prathmann

Don't do this. If the cranks are really French thread (and they probably are) then they're metric and should be 14 mm. Should be easy to tap them out to 9/16" for compatibility with current pedals. The pitch of the two threads is almost identical (20 TPI or 1.27mm/thread vs. 1.25mm/thread) and the diameter is also very close (14.3 mm vs. 14 mm) so the tap doesn't have to do much.