Working on my brothers 85 Peugeot, he has Weinmann 610 on front and 750 on the rear. The straddle cables are pretty shot and measure roughly 150mm, so I would guesstimate them at about 160mm if I were able to stretch it out flat.

Searching online, all I can find are 110mm available on Amazon. VO Orange is out of stock, but I guess theirs are 110mm as well. Just wondering if those would work. I want to say yes, but then again I've never really worked with this kind of brake before.

Just want to know is there a hack or something to make them so I can use the proper length cable? They're the double ended lead cylinder type...

Weinmann straddle cable is part nr. 1270. Six lengths were offered:

If you don't need OEM pieces you can make your own using parts found at motorcycle shops. You can get the barrel-shaped piece in brass that is drilled across the barrel and drilled and threaded through the flats and has a set screw that tightens down against the wire passing through the other hole. Put two of these on a wire and you have a straddle cable, or use one with a standard brake cable cut to length.

Looking in a catalog I see 115 mm and 205 mm available. Check with your LBS, they should be able to order.

A shorter cable will give you greater braking force against the rims, albeit at the cost of longer lever travel. I recommend 110 or 115mm straddle cables, as long as your rims are true and your bearings have little or no play.

As mentioned above, it is pretty easy to fashion your own. You can build one Mafac-style, using a regular brake cable and a pinch bolt.