I'm planning on putting cantilever brake mounts on the back of my SWB
Bentech. The donor bike has the mounts 81 mm apart. My bike's
chainstays are about 143 mm from center to center. I figure,
therefore, that I need an offset of 31 mm from the center of each
chainstay to each cantilever mount.

I'm currently planning on making some tabs from my leftover 1/4" steel
plate, at 15 mmm x 37 mm, and brazing them to the chainstays. I'll
then step-drill holes, 81 mm apart, to fit the cantilever brake mounts
into and braze them in.

My question: do you think that 1/4" steel plate, 15 mm wide, will
withstand the torque that the brakes will place on them, or should I
make the tabs wider? Or, for that matter, should I do something
different for mounting my cantilever brakes?