water is the only thing that is 1 cup and 8 oz, both fluid and weight. a [weight] oz is equal to 28 grams. 8 fluid ounces is the same volume as a cup.
for your ice cream, that means that 67 grams of it should be right at a half cup. the 67 grams is the more accurate way to measure it, but if you want to go by half cups you can do that as well. so if you want to use your scale, you measure out 67 grams of your ice cream and it will be a serving. you could also fill up a half cup measuring cup and that would be a serving as well, and it should weigh about 67 grams.
-google first. ask questions later.