The Authors are not really specific when it comes to portion size.
Most SBers that I know, use 1/2 cup as a serving of starchy carb --- i.e. pasta, oatmeal or rice.
1/2 baked sweet potato is a serving .... 1 slice of bread is a serving.
For my own personal body chemistry, I need to keep the starchy carbs to 2-3 servings per day. You will probably need to experiment in order to determine what works best for you.
I don't put a limit on the LC Lo-GI veggies. I usually have 2-3 servings of fruit a day.
Please be aware that coming off of Atkins the increased amount of carbs may cause you to gain a pound or two.
NOT TO PANIC! This is water weight and your body will get rid of it pronto. It is just an adjustment.
The other thing I wanted to mention was cravings. I find (and this may not be true for you) that some starchy carbs increase cravings and others don't.
Pasta, although acceptable on SB, is a red light food for me. It doesn't take much before I am out of control.
If I over eat bread I can tell it right away ... the ol' cravings kick right in. I try to stick to 1 slice of bread a day.
Again you will need to tweak the plan so that you get the maximum amount of food with the least amount of cravings.
You will quickly get to know how your body responds.
I hope this helps.
molly