dont know if you've considered it, but some time in the future at your leisure you could complete the lines fairly simply by:

1/cutting out the continuing profile on some ply or laid up glassed strips, screw onto the rear form, 2 back to back alum (or glass)2in or so angles separated by the profile thickness - say 1/2in/, drill for a bolt, etc. And you have a retracting skeg.
2/do the same w/ some rudder hardware, but use the profile for the rudder
3/contrast strip(color say) a new back w/a 1/2in box and conceal a skeg in that.

this all probably wouldn/t even look too bad. especially if you make the permanent one and angle the join so it's like a dart into ea other.

-mick