Brian,
Is that 1 mm total (by diameter), or 1 mm from each shoe (by radius)? This sounds like good advice. It just goes to show the things one does not think of on one's first build. Using stock shoes and linings, I have found that I get a chattering at slow speed or when walking the bike. I think this is because the a small area on the leading edge of the back shoe (on the front drum; 8", 1/2-wide) is contacting the drum. At riding speed there is probabaly not enough friction (by comparison to speed) to create the chatter. I think this will go away as the offending area wears away. While turning the lining round is probably the only choice, the single cam action, with just a pivot at the opposite end, dictates that the brake linings are not concentric with the drums when the brakes are in use. I am no expert on the evolution of motorcycle brakes. I suppose that this lack of concentricty is accounted for in bikes later than '55.
Richard