On the master chart for butter cakes on page 490, Level 6 the rectangular pans make only one layer.also baking time should be reversed, i.e. 35 to 45 minutes for the 13 by 9 inch rectangle, 40 to 50 minutes for the 18 by 12 inch rectangle.
page 443, Equivalences & Substitutions for brown sugar:
The closest approximation of light brown and dark brown sugar is the following. The weight will be the same but the amount of molasses is slightly higher and more similar to Muscovado.
1 cup/217 grams light brown sugar=1 cup/200 grams granulated sugar plus 1 tablespoon/15 ml/20 grams light molasses
1 cup/239 grams dark brown sugar=1 cup/200 grams granulated sugar plus 2 tablespoon/30 ml/40 grams light molasses