Years ago I bought some Keil Line brake shoes to put in plastic O Scale trucks that were meant to add a little more detail to the things. They worked but were a little thick and did not really have a lip to hold them in place. Fast forward to now and I have a source for these made better than before. The question is, are people still using plastic Athearn trucks, with or without adding steel wheels to them, and if so, what would be a reasonable price for the brake things? The worst part of installing them is when the springs slip and go flying off into the future, so best to use the thread method to put the springs back in place when adding them to the trucks.
Also, I have more than a few old diecast and even some brass freight trucks that are missing brake shoes, all it would take is a little redesign to make the planks for 2 springs instead of 3. Worthwhile?