Unless otherwise informed by your doctor, grapefruit seems to be the only fruit to avoid.
You can replace it with 1/2 an apple, or pear, or a whole orange. ( around 15 grams of carbs ).
I was interested because for 5 years I was on lovastatin, and no one ever told me not to eat grapefruit. Luckily, I don't like them anyways, and stick to berries, and apples.
40-30-30 is just 10 % less carbs, and 10 % more protein. It is no more strict than the SP 50-20-30. No one is getting exactly 40-30-30, but we should try, just as you should when eating 50-20-30. You aren't supposed to eat all carbs for breakfast, and a slab of meat for dinner on the SP guidelines either. You ARE supposed to eat 3-5 meals that are as balanced as possible. Often snacks are hard to do this with, but it is a goal you should try for.
In that regard, it is no more strict than any other plan. Also, all that was really asked, was how to replace a serving of grapefruit. I think we can answer that quite simply by saying to eat another fruit, that gets the OP 15 grams of carbs to replace the grapefruit, without lecturing about the rigidity of a diet that is almost identical to the one most Americans should ( but don't ) follow according to the experts.