Welcome to the Bike Forums. Like you, I am a bit of a Motobecane enthusiast also. That said, even though the OP's bike is a beauty, tastefully done and a treat to view, it is not a restoration in my mind. Except for the incredibly dangerous weld the caliper arm thing, well done. There is a lot to properly welding aluminum and with something as critical as the caliper arms - forgetaboutit!
What I found that will help extend reach is to modify a front brake caliper alloy washer. These can be filed to a wedge shape, which when rotated, will safely but only slightly, extend caliper reach. Were I the OP, I would get those modified calipers off the bicycle before riding it again. Trust me on this - crashing can really hurt and for a heck of a long time. I endoed my bike in 2000, broke my neck in two places and my neck still expresses different levels of discomfort (pain) to this day and even as this moment.
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"98% of the bikes I buy are projects".