Swingle described maximum growth of the northern strain as > 2/year. This kind of growth occurred when the LMB were unable to reproduce. He thought large numbers of BG exuded a hormone that suppressed their own (and the LMB) stimulus to spawn. Others thought the BG harassed the nest to the point they all ended in failure. It may not be black and white and may actually be grey. In any event, without the offspring intercepting their gravy train ... adult LMB may achieve their maximum growth potential.
It may not be possible to achieve 8 lbs in 3 yrs. On the other hand, if the conditions are set for maximum growth and 8 lbs was achieved in 4 or 5 years ... hey that's awesome.
It's important to understand that under normally recommended stocking rates, the achievement of 8 lb LMB may not happen even with dedicated effort in management. Typical stocking rates are designed to achieve LMB reproduction the year after stocking and are also intended to prevent BG overcrowding. Anything done to maximize BG reproduction and delay LMB reproduction will serve to rapidly grow LMB. A couple of things that will do this:
1. Fewer LMB at the initial stocking (less competition)
2. A limited number of adult BG. (Lots of food for adults to induce repeated spawning and lots of room for little BG like in a BG hatchery pond)
This would maximize the LMB growth and probably delay LMB spawning for a couple of years or more. If LMB are sufficiently restricted in the initial stocking and the pond is basically a hatchery in the beginning I think it is almost a foregone conclusion that some of LMB will attain weights of 8 lbs though it might take a year or two longer.
But to this I digress. It might be a lot more fun to try to do it (under a typical stocking plan) and fail than to actually achieve the goal. Given all the trophy fish will be the same age, there won't be many of them and the BG won't be large. Might be more fun to cull LMB and catch some nice panfish to fry. Just saying ...