Agree that the T67A has very different charactristics depending on Centre of Mass. Some years ago we hired one for basic spinning and aeros instruction. The aircraft has a lowish mass limit; after weighing the crew, we used to calculate the fuel load pemissible and then measure it carefully into the tank (which is well forward of the Centre of Mass), finally checking the fuel load with a dipstick. With a heavy student, the fuel load had to be low and this caused an aft C of M. Hence stalling and spinning were markedly more lively than with a lighter student, more fuel and a forward C of M.
I thought that the T67A was excellent for teaching stalling and spinning, but awful for teaching aeros as too much time had to be spent milking the throttle to stop the engine from over-revving. It also has an utterly appalling roll-rate; nothing like as good as the Bulldog. Hence you only ever see vertical or flick maneouvres at air shows; large aileron deflections merely cause aileron snatch and buffeting. How on earth this thing was ever accepted for military training (beyond the very basic stage) is quite beyond me!!