So I converted one of my bikes to a townie sort of bike for my SO, flipped northroads, short tall stem, cushy spring seat, etc. I didn't want to leave her with center-pulls because they look tacky, and because I didn't want to fit a center-pull cable stop on the front so I made some MAFAC Racer's into a dual pivot sidepull and they work surprisingly well with weinmann upright bar Aluminum brake levers (circa 1969). The only modern piece is a 90* hard-line from a newer tektro V-brake for the front.
I ran a cable from the lever, into the 90* piece, then through the yoke wire quick-release, then attached it to the other quick-release yoke wire thingy. This only works because the MAFAC Racer's have an adjustable Yoke Wire.
Has anyone ever done this? I'm honestly surprised that the mechanical advantage isn't way off. I didn't have any other sidepulls laying around to use and I think I might like this setup more than most old sidepulls/upright bar lever combinations.

I've seen pics of this setup before. Seems to me you lose a lot of mechanical advantage like this.

I love centerpulls, so would never bother to try and switch to sidepulls, but I'd still like to see photos!

Photos please! BTW, modern BMX U-brakes and contemporary Campagnolo time trial bike centerpulls, use this cable routing scheme for certain applications.

The mechanical advantage will be in proportion to the ratio of cable pull to combined brake shoe displacement. Note that this ratio may change slightly over the range of motion, but probably not very much. Should be easy enough to measure both setups and compare. Not taken into account for overall lever effort vs braking force is any friction in the system. I would expect the 90deg hard line adds an incremental amount of friction versus the standard centerpull configuration.

I'm interested in pics, as well.

Sounds like it is mechanically a mini v-brake that looks like a u-brake.
clever