The Zone is horrid for mass gain. Fat should come from ANIMALS, not plant sources. If they want mass gain you have them eat everything in sight and tons of milk. You don't put them on a calorie restrictive diet (Zone) and expect huge mass gains. If you want em to go more Paleo, great, I do that myself, but don't put them on this measuring crap because they won't follow it when their body is trying to produce muscle. They will eat because their body is telling them to do so to build.
Big dudes eat big meals, and they lift big. Lets not make this rocket science because it isn't. SS is great as a starting point. But what are their goals? Why not teach them the lifts (which doesn't require SS), and put them on a mass gain program, you can pick from just about anyone one of them out there. They all have tons of deadlifting, benching, pressing, pull-uping (not a word), and squatting. They need to balance volume and intensity to produce muscle.
You've started a venture that is harder than making a fat person skinny. I wish you luck.