What cotter pin, what stopper.
The cotter pin that holds the long thin linkage bar should be readily accessible.
The spring that provides tension on the spindle is a greater pain in the ... if you have to remove it.
You should be able to remove the cotter pin, take off the rear bolt for the rear brake torsion bar then remove the linkage.
If you can't get the cotter pin out, I think you're going to have to take the wheel and swingarm off.
Free bump to the top cuz I'm sure some other's will have more input