How many more bluegill and forage fish would I need to support the predator fish?
See my post above your question. That is where my answer is. Look at the ratio I put there. The bigger number is the number of bluegill you should have stocked for every LMB.
Here's some math for you. A single LMB needs to eat 10# of forage fish to gain 1# in weight. That's when they are young and small. As they grow in age and weight they need to eat more and more fish per year just to survive, and way more fish to put on 1 pound in weight. Think of a human. How many calories do you need to eat per day to stay the same, vs how many calories a baby needs to eat to stay the same weight? Fish are no different.
A LMB needs fish to eat that are roughly 1/4 to 1/3 it's body length or it's wasting too many calories chasing down smaller fish to eat. A LMB does NOT catch a fish every time it tries to, so that is more wasted calories.
You stocked 75 2"-4" LMB. At that size, they need fish in the 5/8"- 1.3" range to eat. As they grow the fish they need to eat have to be proportionately larger.
Bluegill that are 1"-2.5" in length weigh 3-9 pounds per thousand fish. Bluegill that are 2.5"-2.75" weigh 10-14 pounds per thousand. Bluegill that are 2.75"-3.5" weigh 15-24 pounds per thousand.
So, with that information you should be able to do the math and figure out how many fish you need to add, and what size they need to be..