No that would exclude the gussets, if the pattern is the same. A 58 is 30” with the gussets, which means the 58G is 3.5” wider. A 56 is 29” with the gussets, so if you add the same 3.5”, a 56G would be 32.5” with the gussets.
I’ve never measured (nor seen) a 56G, I’m only guessing based on the measurements of a 56, 58, and 58G.