Yes the plans show two shelves. One for each seat.
The HD was designed as an Oregon style boat. To fish someone behind the rower the front seat needs to be able to slide pretty far forward. That's also why the HD plans so such a small deck up front. Most drift boat plans show a big front deck with the front seat pretty far back.
I like to be able to squeeze the front part of the payload way way forward, so the boat still trims and balances well with a rear sitting or standing passenger.
To do that with one shelf is hard. If the one shelf is at the right height for the rower it would be pretty close to the floor by the time you got to the front seat position.
You could get some big refrigerator size cardboard boxes and cut them up to mock up some shelf like things. Maybe all one shelf that raises up near the front seat, like a stepped concrete foundation on a house.