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.

I switched from clips and straps to SPD MTB pedals. Didn't notice any performance advantage, but there was improved comfort on long rides. The clips and straps would push down on the tops of my feet and start hurting after 50 miles or more. The shoes I wear with the SPD pedals are very comfortable for walking and I've even used them on some extended hikes. Never had an issue with being unable to get my foot out of the clipless pedals in time but did have a couple tumbles when using clips and straps.