Hi M N-
I’ve read a lot of different opinions about what type of diet working breeds need. It seems that a lot of people who hunt their dogs or compete in dog sports will use a performance/sporting food during the season and then go back to a normal maintenance diet during the off season to prevent weight gain and keep them conditioned. You have to feed for the energy expenditure of the dog.
Typically performance foods are going to be a 30/20 formula, but still have a good amount of carbs for quick energy conversion. I believe Victor and SportDog both have performance formulas. I see you are interested in grain free, but I would highly consider a grain inclusive diet as many grains actually have better bioavailability.
As far as feeding for a large breed puppy, he is just shy of the 18 month mark at which he could go on to an adult food and at this point he should be able enough to control is calcium uptake enough that the main focus should be keeping him in condition to hunt him. While a 3 on BCS is not terrible, 4 would be better/ideal. GWP/GSP are lean by nature, but the standard is not that of a Greyhound, Poodle etc.
