It depends on Sarge's activity level. 3 pounds seems like a little much to me but it may not be if he's a really active dog with high metabolism.
I use Lauri's Guide as a jumping off point - it's spot on for my muttpuppy, but I think my GSDs metabolism is a bit slower so I have to feed her quite a bit less than the calculations I get with Lauri's formula.
How Much to Feed
My GSD was severely underweight when we rescued her at 2 years old. She originally weighed in at 59 pounds after giving birth to a litter of pups - you could see her ribs, it was heartbreaking. We got her weight up to around 90 pounds feeding about 26-28 ounces a day...90 pounds turned out to be much for her so we then worked to take some of that weight off. Now she eats around 22 ounces a day and has leveled out between 75-80 pounds and looks great and has tons of energy.
She gets between 9-11 ounces of raw meaty bones (usually turkey necks or chicken backs - really cheap by the 30 pound case at the butcher) and between 9-11 ounces of a muscle and organ meat mix I get through a raw feeders coop.
You definitely need to add some organ to your mix, specifically a secreting organ - like a liver or kidney (gizzards and heart are considered muscle meat). If I wasn't feeding a muscle and organ mix, I'd reduce my muscle meat by 2-4 ounces and feed 2-4 ounces of secreting organ each day.
I also supplement salmon oil - although we recently got a fish monger who sells fish heads and bits for next to nothing so I may switch to that if my muttpuppy can figure out that he needs to eat the fish head and not play with it (my GSD is smart as a whip and has that part figured out!).
Good luck!! Looks like you're doing a great job.