Clayton, here's the sequence for polishing any of your parts, brass and steel. First, in the case of the lock, you file everything flat and true. Then you use abrasive cloth to remove the file marks, using a file or piece of wood to back the abrasive. Start with 80 grit, then 120, 180, 220, 280, 320, 400, 600. You can go for a mirror polish with 800, 1000, 1200, but it's a military rifle, so I didn't bother. For the barrel, 180 grit polishing lengthwise with a block of pine carved into a concave shape. Bakers barrels were browned, and 180 grit is lots fine enough.
Flintfan is correct. The lock gets two holes drilled with a tap drill, and the holes are threaded for the lock "nails".