Hi There Chris,
Nice project you have there, I think the minimum size of a Marblehead is 50.2 inches, I would remove the old gear and start again (if you can) the cheapest option is to use a powerful sail servo (20Kg pull) and arm setup, or drum system. Be aware digital servos may not travel full rotation if you don't have a digital transmitter with the options to increase travel over 100%.
Best thing join a club and take it a long and get some advice, as to what to do and how much it will cost!
I would work on a nice cabin, the rest looks good!
Don't worry about it not being a Marblehead, unless you want to compete, most clubs have non class racing where any boat can sail against each other.