Yes, the squirters are stamped with the size. They generally go up in size 2-3 #'s at a time. Next size bigger than 28 is 31, then there is 32, 35, 37, 40, 45. You can also make custom sizes using a hobbyist pin vise and small drill assortment(Drill #'s 61-80, 61 is something like .059", 80 is like .013"). I've taken many years accumulation of 25's and made a bunch of custom sizes, marked with an ingraver.
You may need to change to a different pump cam also, the Holley cam assortment kit is inexpensive and good to have. You'll just have to experiment with it.