Cut a couple pieces of 80 grit sandpaper into widths that fit in the drum. Double stick tape the sandpaper on the full interior circumference of the drum and install normally. Start the bike on the center stand and put into gear and let the wheel spin and depress the brake. Repeat a few times.
Pull the brake off and inspect the shoes. They should have sandpaper wear on the full arc of the brakes. If not, reinstall and repeat. If they do, Give everything a good clean and relube, and reinstall.
This will help with arcing and having good strong brakes from the get go.