40 lbs of 8 inch largemouth bass extrapolates to 300-400 fish. That's way too many. You trade problems, plus the cost would be several thousand dollars. If you have 40-50 pounds of adult lmb per surface acre, they can control bullheads. As most people know, lmb will eat whatever fits into their mouths. I have used lmb to control bullhead populations. It takes a fairly long time, depending on the population of bullheads, their sizes and numbers.
HSB, on the other hand, can do a reasonable job, also. But, don't start with small ones, if larger ones are available. Mouth size is the key to solving this problem. One huge advantage to HSB...they will readily take fish food, so as they effectively do the job of eating young bullheads, they grow quickly on fish food, and when the job is done, you can continue to feed them out of competition for other forage fish. LMB will not be taken out of competition for forage fish.
One thing I always preach...learn the life histories and lifestyles of each fish which might play a role in your project. Know how they eat, how they spawn, how they interact in a community, how they eat...then you can make the best decisions how to manage your fishery.
