The pork ribs will need to be chopped into short lengths to make them quicker to cook and easier to eat, especially if you are eating them Vietnamese-style with chopsticks. Unless you are handy with a meat cleaver, it is best to ask your butcher to do this for you. For pork baby back ribs, I often just ask the butcher to cut a rack of ribs down the middle. For a rack of larger sized pork spare ribs, ask your butcher to cut them into 2 cm to 4 cm lengths (1 inch to 1.5 inches).
To convert from cups to grams, and vice-versa, please see this handy Conversion Chart for Basic Ingredients.