Your dimensions must be for the linings of the drum brake shoes. You don't need to worry about that. The company who makes the drum shoes takes care of it. Once you get a set of shoes, you need to notice that they have different lengths of lining (dimensions above). Put a shoe with the short lining (primary) at the forward side (whether front or rear wheels) and a shoe with the long lining (secondary) at the rear side. That is because the rear shoe is pressed on by the front shoe (not all drum brakes, but in ours), so the rear shoe has a larger force pressing it into the drum.
I just took apart the drum brakes in my 64 Valiant. I expected severe wear since it was stopping poorly and clunking. It had almost new parts assembled wrong. Both secondary shoes on the left front and primary shoes on the right front. They had a pair at each rear, but reversed. The self-adjusters were on the front sides of each brake, since they had all the L & R parts swapped (L = driver's side). Amazing since those parts had L and R stamps. I also found grease all over the shoes of the left front. It appears they packed wheel bearing grease in the recess in the backing plate that is intended to catch any grease that gets past the seal (I think).
Moral of the story - don't touch your brakes unless you get good instructions and can follow them. For any parts replacement, carefully study the parts and consider all the ways you can install them wrong, then find out how they should go if any questions.
