The new shoes match the drums pretty well. The shoes appear to contact the inside of the drums along 80% to 90% of their length. At the end that is not in contact the gap between the friction material and drum is less than 0.010". If I put sandpaper on the inside of the drum the contact area is going to decrease so I think I'll just try the shoes "as is" rather than improvising an arcing technique.
Unfortunately, I can only do so much prep work at night after work. Installation and a test drive will have to wait for the weekend.
I'll keep you posted.