Gaining weight this method would work, yes. And your conditioning will be phenomenal by the time you're done.

But you're looking to consume about 4000 calories a day if you hope to gain weight this way.

You can eat anything, that you feel will be able to help you sustain your energy levels towards the entire workout.

Personally, my pre-workout food is a whole plate of rice, 2 drumsticks, 2 fried eggs and I'll usually chug down a oats+protein shake 30 minutes before training. And when I'm done with my main workout and supplementary workout, I'll take a bar of Snickers (just a habit) and finish off.

My training does take about 2.30-3 hours, so I'll need as much calories as I can possibly get.