So I got this ok old (probably mid 70's but thats a guess) Atala frame basically for free (I had to help move a couch in exchange) and so I decided to convert it to a fixie (I always need a project and my other bikes were finally 'done'). Anyway, I was going to replace the cranks until I realized that they were 'stronglight' French cranks and that my crank puller wasn't going to work. not wanting to hammer them off, i decided to leave them on. The pedals are complete garbage though, so I wanted to replace them, and last night I went to take off the old ones and realized that my pedal wrench was too small (its 15mm). These appear to be about 17mm (but my 17mm wrench can't fit in between the pedal and the crank arm, and so I will have to buy a real 17 mm pedal wrench, and hope I am right about the size). Tomorrow I'm placing a wheel order and thought I'd throw in some pedals while I was at it, but now I am concerned that like everything else with these cranks, I might run into some sort of weird French sizing issue. According to Sheldon, old French cranks sometimes do have another pedal sizing, but I have no idea how or what I should measure. Does anyone have and experience or advice with French cranks?
the picture below is not my bike, but the cranks look just like that in case that provides any clues.