Hi
LM,
Of course you are correct, I was being too simplistic in my description. It seems that the wing-fins were used to generate side forces to simulate cross-wind landings (if you zoom-in on the one in your photo, the lower surface looks like it has a gust-lock fitted, so I guess it may be all-moving) . They also had an unmanned cockpit that could be fitted in place of the one shown. See below
Factsheets : Convair NC-131H Total In-Flight Simulator (TIFS)