I know nothing about building a manual dough sheeter, but have been following this thread. I don’t know if these pictures will help you or not, but these are old candy machines that were used to make stick candy. They were hand cranked and a piece of warm candy was then placed though them. Just thought I would post the pictures in case you could get an idea from them, on how a manual dough sheeter might work. These hand cranked candy machines could be adjusted up or down for the thickness of candy and they just have two gears. I had planned on some point in time in trying these out to see if they would work out for dough and something like rolling out dough for breadsticks, but haven't had time to clean them up and try them.
Norma