The original recipe called for brown sugar. Yes, this is totally acceptable. I've used coconut palm sugar- it has a few added nutrient benefits (fine, it's still sugar) The flavour is wonderfully like brown sugar- that caramel, warm sweetness.
My mother in law stated on the card that this could make 54 squares. This is indicative of the many pot-lucks and get togethers they attended out west, and how moms always brought enough to share!
If you actually want to achieve this number, really ensure that you have let the pan cool entirely before cutting into it, or else it will be more crumbly, than nice neat squares.