First, take the shoes off and lay them in the drum to see if there is a match to the radii. If not, sand the shoe linings until they match the drum. You can use a belt sander or glue 80 grid sand paper to the drum and move the shoes inside the drums. The belt sander will also be a good tool to add the chamfers. Make sure everything is right with the brake such as the cam and wheels. I assume you have the adjuster all the way out.