The brake pedal is attached to a brake pedal shaft. I would install the brake pedal shaft, spring & other stuff from a 650B. As previously noted in your other drum brake topic, the 650B & SR have the same brake pedal, and from comparing their frames on EB, it looks like the pedal is attached in the same location, so it seems like a stock type conversion would be possible. for safety.
Here is a picture of my current set up.
Hope the pics are clear enough
U can see my brake shaft "circle barrel holder" is in the down position
It order for it to pull on the rod proper it would need to move upward
But when it moves upword to achieve the proper motion . the brake shaft (which the brake rod slides through the end of)
Hits the swingarm