Interesting. I'm assuming you've confirmed the crank ends are French threads. When I received my mostly original equipped '72 Le Champion, it came with a Stronglight 93 crankset (170mm arms / 42-52t rings), threaded for 9/16-20tpi pedal axles. Has the original Campy N.Record shift group, pedals and Tipo hubs. Oddly though the brochure specs Lyotard pedals and who knows what pedal thread; could be either French or English. Although like I mentioned, mine are 9/16 x 20. Then again, the 1972 model year has a Swiss threaded bottom bracket. Funke'

Back to the crank. The Stronglight 93 were plentiful and made for many years, pedal ends available in the 9/16x20tpi and also French thread 14mm x 1.25. Perhaps you should set your crank aside and just get the English threaded version. Don't mess around with rethreading.

Onto the pedals: If by chance you're committed to going with a vintage clipless, they do exist but rare. IMHO, I'd think they'd pretty nutz to use, but thats half the fun riding this old stuff. For reference, check the online Speedplay pedal museum and then shop fleabay. (Don't forget the mate cleats!)

I get where you're going and like the same idea but if you want to sort of look vintage and ride sensible clipless, you can't go wrong with Shimano PDM323. Get the chrome steel cage version. Also if you want to jazz them up, grind and polish out, they easily dismantle.

(p.s. I ride my LeC off-road and gravel trails, using the original pedals and toe clips. I wear 1st gen Vittoria mtn. bike shoes designed for SPD cleats.)