Since you're already fasting and doing hard labor, you'd probably get a lot out of drinking 1-3 pulses of MAG-10 throughout the period where you're working. I've done it, and at the end of the week I was going just as hard as I was at the beginning, same goes for the end of the month. I've tried BCAA instead of MAG-10, it helped, but it just isn't the same.
The type of work you do sounds close enough to what I was doing. This isn't what I did, but it's what I would do when faced with the same problem:
-If I'm expecting to do something I could compare to sprinting. Indigo-3G if I didn't have it before dinner yesterday, Flameout, 1-2 Plazma
-If I'm not going to be doing that kind of thing, I would probably just drink MAG-10 as I was coming in to work.
Pack 1-3 MAG-10 pulse (or servings of Plazma if you're really going to be kicking ass), drink throughout the day.
Dinner: Indigo-3G if the day kicked my ass and I hadn't taken it in the morning, clean carbs to 'feed' Ingio-3G and make up the calorie deficit (nice plain rice), some healthy meat and superfood/fruit and veg, maybe some peanut butter, coconut oil, etc to cover fats--FA-3 was awesome here.
By the standards of this website, I'm not the strongest, leanest, or fittest, but thanks to aggressive supplementation, I was able to keep up with much, much tougher guys for the duration.