I'm guessing I put on 10lbs of LBM in the last 6 months but it's been getting back muscle I've lost through taking an almost 3 year break. I'm natty for last 3 years, retired well, I've got no financial constraints, but I do have a family, two young daughters. So I've been stuck at 220lbs but my strength and endurance are roaring back with absolutely visible decreases in my flabby areas so I assume recomping considerably. If I get back to 220lbs with visible abs and close to previous bests, that is where I would have to start. And yearly gains past that would be a gift. Heck, maintaining would be a gift at my age TBH.
So if I had to do it natty, and gain the maximum amount of muscle in terms of straight LBM, and no consideration for symmetry or proportions, well hell. I'd just do Mon: squats, squats, squats, squats, more squats, leg press, leg press, rest a day, Wed: bench, bench, bench, cleans, cleans, cleans, clean and press, clean and press, clean and press, again and again, rest a day, Fri: deadlifts, deadlifts, deadlifts and more deadlifts. Track sprints on weekends 100m, 200m. I wouldn't do a concentration-style bbing split at all. Not without juice. I'd apply the shotgun method, not crosshairs. I would be looking to compound exercises which increase growth factors (chemically) naturally. And a ton of rest and clean nutrition. Old school? You bet. I'd vary hack squats, inclines, declines, weighted dips, straight overhead presses, etc, but the idea would be the same.
Nothing did more to change my entire morphology and bodyweight than making progressive strength training the only thing that mattered.
It's an interesting proposition, and maybe I'm just subjectively hearkening back to my heyday, but that's what I would do.