dorset john

CofG will probably be spot-on (there is a slab of metal pre-installed in the tail).
The stab can be reinforced by drilling a 2mm hole just in front of the stab upright and inserting a 2mm carbon rod and cyano'ing it in. The rod sticks out the bottom of the stab and is inserted in a matching hole drilled in the fus' stab base.
Do use post type rudder horn to account for the twisting motion. I can manage flat-out knife edge loop with this configuration.