I would recommend making the main mast roughly the waterline length, and the mizzen, about 1/2 that. Cut the excess off the bottom of the masts, you might not have to do any further work on them to make them look good. I would also suggest reducing the "bulk" of the stem, that's a lot of wood beneath the bowsprit.
This 1/87 scale, waterline model, 62' Ketch, Jenan III, was bashed from a Lindberg "Fishing Schooner Elsie" hull, with scratch built cockpit,cabins,masts,and rigging.
Pete