Straddle cables on my Puegeot mixte w/Mafac Racers is probably 10".
Straddle cables on my Puegeot mixte w/Weinmanns is probably 7". (It came with Mafac's, but not Racers)

afilado did a great conversion to a y-connector from a cantilever brake setup.

My guess is neither of my mixte's would be able to handle that long one from Loose screws.

I think the caliper type would determine if you can cut to length.

Some of those calipers will accept a regular brake cable, disc end, and then you adjust it on the other end.
Some don't.

You may be better off buying another caliper, used, from eBay.