FYI, Brake cables are thicker than the derailleur cables for obvious reasons. I would do this only as a temporary fix as these single ended straddle cables are available online (as are double ended [with non-Mafac ends]). I would assume you have Racer calipers as the Competitions have round cable ends on each end(and are about $50 apiece now!). FYI, the new ones can be modified to fit Competitions.
I think Loose screws had them. Regular double-ended brake cables might be able to be shortened as well ..... if I'm remembering the one barrel end fitting. Otherwise those are still available. It's only the ones with balls at each end that are impossible to find.
Post some pics if you can. I just posted a pic of mine finished on the blog. I 'll add more to the blog about handlebar wrap with mafac half hoods, etc. when I get time.
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