I worked in a feedmill for 7 years (after school, weekends, summers and full time after graduating high school). It both helped and hurt my progress...I was lifting hundred pound sacks all day long, lifting up to 240lbs (3 80lb bags of rock salt) from the floor to my shoulder, to carry it and load it onto trucks and doing a tremendous amount of endurance work and odd lifts but never got above 200 lbs lean (at six foot with a large frame), Even eating up to 6000 calories a day I was never able to get the "bodybuilder look" just a fit laborer look. A big part of my problem was working out too often on top of labor I did as well as too intensely with too many exercises and reps.
The three days/week workouts you mentioned would be certainly be better than the 6 days a week splits I ended up doing at 18 (thanks to believing bodybuilding mags). After looking back at it a couple of decades later I see that the gains that I made were mostly from the times I lifted less frequently, using the big compound exercises (squats, deads, bench, dips and pullups) and lots of rest to keep from overtraining (during the school year when i wasn't working all day long) Don't do a lot of exercises in the gym that mimic the movements you do at work. Keep in mind that labor with up to forty pounds is fantastic for core stability as well. Hope this helps..