I thought keeping it simple like this would be easier - <<<
Simplest way would be to put wife and daughter in field, while you drove the hauler/wagon.
If you want to test your idea to push it with your feet, why not
use scrap lumber, and make a rough shelf if you want to be higher[under the seat, storage for small tools], or a couple scraps that will bring it up to the metal edge of the back, that angle iron, will hurt, throw an old couch cushion on it, or a good pillow, tie it down, [granny would use baling wire] and work using it for a day or two.
If it is what you really want, then you will know exactly what you want to do.
Love the antique steam wagon, you don’t need to dig it down in a trench, you can steer it and the wife and daughter can do the work, hand you the produce.
Hey, I get enough dirty looks whenever I suggest hitching wife and daughter to a plow... Don’t want to dig that hole any deeper... LOL